Fix Klaviyo CSV Import Errors: Consent, Phone and Suppressions (2026)

Quick Answer

Klaviyo CSV profile uploads fail for four predictable reasons, most commonly showing "Invalid phone number format" or silently skipping rows with missing consent timestamps.

Klaviyo enforces strict validation on phone numbers, consent fields, suppression list formatting, and duplicate profile detection. Unlike some email platforms that accept messy imports and clean data internally, Klaviyo rejects or silently skips any row that doesn't meet its schema — which means failed campaigns and incomplete lists with no obvious explanation. Every issue here is fixable before upload, without sending your customer data to a third-party cloud service.

Generic CSV import guides treat consent as a checkbox. Klaviyo's consent model requires ISO 8601 timestamps with timezone, separate email and SMS consent fields, and a Source property that affects deliverability — none of which appear in cross-platform guides.

Each error type was reproduced using Klaviyo's profile import and suppression list import modules, March 2026.

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What Klaviyo's Error Messages Actually Mean

"Invalid phone number format" — Phone number doesn't conform to E.164 international format. Klaviyo requires + followed by country code and digits — no spaces, dashes, or parentheses. Fix the phone column before re-importing.

"Consent timestamp is required" — Your list includes an SMS consent field but no corresponding timestamp column. Klaviyo requires both fields together for compliance. Add the timestamp column or remove the consent field entirely.

"Email is invalid" — Malformed email address in the row — missing @, extra spaces, or an invalid domain format. Filter and remove or correct invalid emails before import.

"Profile already exists with conflicting data" — A Profile with that email address already exists in Klaviyo. Depending on your import settings, the row is either skipped or used to update the existing Profile's Profile Properties.

"Required property missing: $consent" — Your CSV is missing the $consent field required for Klaviyo's Marketing Activity compliance tracking. Profiles without $consent set cannot be added to active sending Lists & Segments.

Rows silently skipped during import — Most commonly consent validation failure or duplicate detection. Always check the import summary after upload — Klaviyo shows a skip count with reasons in the results screen.

Suppression list import fails entirely — File encoding or formatting doesn't match Klaviyo's suppression list requirements. Suppression files must be plain UTF-8 CSV with a single email column header.

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Klaviyo CSV Import Error Quick Reference

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Table of Contents

• Why Klaviyo CSV Imports Fail
• Error 1: Invalid Phone Number Format
• Error 2: Consent Timestamp Missing
• Error 3: Suppression List Encoding Failure
• Error 4: Duplicate Profiles
• Fix Multiple Errors at Once
• Additional Resources
• FAQ

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This guide is for: Email marketing managers and ecommerce operators importing contact lists, suppression lists, or profile updates into Klaviyo via CSV.

Already know which error you're hitting? Jump directly to the relevant section above.

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Why Klaviyo CSV Imports Fail

Klaviyo enforces compliance-driven validation on every import. Phone numbers, SMS consent fields, and suppression lists are all subject to strict formatting rules that reflect TCPA and GDPR requirements — not just Klaviyo's preference. A phone number without a country code or an SMS consent record without a timestamp can create legal exposure, so Klaviyo blocks them at import rather than accept potentially non-compliant data.

Unlike HubSpot or Mailchimp, which often accept messy data and flag issues post-import, Klaviyo rejects or silently skips non-compliant rows before they enter your account. The result is a list that looks imported but is missing records with no clear indication of what failed.

The import summary screen after each upload is your most important diagnostic tool. Always review it before assuming an import succeeded.

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Error 1: SMS Compliance Prerequisites Not Met

Klaviyo's phone number validation catches two distinct failure types: formatting errors and compliance gaps. Formatting errors are correctable in your CSV. Compliance gaps require action in your Klaviyo account before any phone number will be accepted for SMS sends.

Formatting requirement: E.164

E.164 international format requires a + prefix, country code, and subscriber number — no spaces, dashes, parentheses, or dots. (415) 555-0123 fails; +14155550123 passes.

Fix formatting errors:

1. Strip all non-numeric characters from the phone column except the leading +
2. Add the country code prefix if missing: +1 for US/Canada, +44 for UK, +61 for Australia
3. For bulk reformatting across 50+ country formats, use SplitForge Data Cleaner to standardise to E.164 automatically — no upload required
4. Verify with a sample of 10 rows before re-importing

Compliance prerequisite: 10DLC and toll-free registration

Phone numbers that pass E.164 formatting can still be suppressed by Klaviyo if your SMS sending setup is not registered. US SMS requires 10DLC (10-digit long code) brand and campaign registration through Klaviyo's Brand Registration portal. Until your A2P (Application-to-Person) campaign is approved by major carriers — AT&T, Verizon, T-Mobile — phone imports succeed at the file level but outbound SMS is carrier-filtered before delivery.

For toll-free numbers, toll-free verification is a separate process from 10DLC registration. Unverified toll-free numbers are throttled to 3 messages per second and subject to MNO (mobile network operator) filtering that can suppress delivery entirely.

The $phone_number_region field:

Klaviyo uses the $phone_number_region column (ISO 3166-1 alpha-2 country code: US, GB, AU) for carrier routing and SHAFT compliance checks. SHAFT categories — Sex, Hate, Alcohol, Firearms, Tobacco — are subject to carrier-level restrictions that Klaviyo enforces before sending, independent of whether the phone number is formatted correctly. Importing without $phone_number_region causes Klaviyo to default to US routing rules, which suppresses international numbers that would be valid under their own country's carrier regulations.

Klaviyo's accepted phone formats:

• +14155550123 (US — E.164, 10DLC-registered sending domain)
• +447911123456 (UK — E.164 with $phone_number_region: GB)
• +61412345678 (Australia — E.164 with $phone_number_region: AU)
• (415) 555-0123 (formatting violation — parentheses not accepted)
• 4155550123 (missing country code prefix — Klaviyo will not infer +1)

For Klaviyo SMS infrastructure setup including 10DLC registration and toll-free verification, see Klaviyo's SMS sending documentation.

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Error 2: Consent Timestamp Missing

Klaviyo's "Consent timestamp is required" error appears when your CSV includes an $sms_consent field but doesn't include the corresponding $sms_consent_timestamp column. Klaviyo requires both fields together for its Marketing Activity compliance tracking — consent without a timestamp is treated as non-compliant and the Profile is added to your Suppression List rather than your active list.

This error is most common when exporting from a platform that records consent as a boolean (true/false) without capturing when consent was given, or when consent data is added manually to a spreadsheet without a matching timestamp.

Klaviyo-specific consent column format:

Email,First Name,Last Name,$email_consent,$email_consent_timestamp,$phone_number,$sms_consent,$sms_consent_timestamp,Source
[email protected],Jane,Doe,true,2026-05-06T10:30:00-04:00,+15551234567,false,,Onboarding Form

Fix option 1 — Add the timestamp column:

1. Add a new column to your CSV named exactly $sms_consent_timestamp
2. Format timestamps in ISO 8601 with timezone offset: 2026-01-15T10:30:00-05:00 — Klaviyo requires the timezone, not just the date and time
3. Use the actual consent collection date if known, or the date of your data export if consent was collected through a verified opt-in flow
4. Add a matching $email_consent_timestamp column if your CSV also includes $email_consent
5. Verify the timestamp format matches Klaviyo's requirement before re-importing (see Klaviyo's CSV import documentation for field naming and format rules)

Fix option 2 — Remove the consent field:

1. If you don't have reliable consent timestamps, remove the $sms_consent column entirely
2. Import Profiles without SMS consent data — they will be importable but excluded from SMS sends
3. Collect SMS consent through Klaviyo's own sign-up forms going forward — this captures timestamps automatically in the correct format

[Screenshot: Klaviyo import field mapping showing $sms_consent and $sms_consent_timestamp columns]

Why Klaviyo enforces this: TCPA regulations in the US require documented proof of when SMS consent was obtained. Klaviyo's validation prevents you from importing consent records that couldn't withstand a compliance audit.

Edge case — Consent timestamp timezone requirement:

Klaviyo requires ISO 8601 format with timezone for $email_consent_timestamp and $sms_consent_timestamp. Other platforms accept date-only (2026-01-15). Klaviyo requires 2026-01-15T09:30:00-05:00. Missing the timezone causes silent suppression — Klaviyo processes the row but marks the Profile as unconsented and moves it to the Suppression List without surfacing an error.

Edge case — SMS vs email consent separation:

Klaviyo separates email and SMS consent at the Profile level. A Profile can have $email_consent = true and $sms_consent = false. Importing a CSV with only one consent column (a Mailchimp-style single consent flag) and mapping it to both $email_consent and $sms_consent silently overrides whichever consent state was set previously. Keep $email_consent and $sms_consent as separate columns in your CSV — do not map a single consent field to both.

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Error 3: Suppression List Encoding Failure

Klaviyo's Suppression List importer is stricter than its profile importer. A Suppression List import that fails entirely — rather than skipping individual rows — is almost always a file encoding or column header problem.

Klaviyo's Suppression List requires a plain UTF-8 CSV file with a single column named exactly email. Any deviation — a BOM character at the start of the file, a different column header, additional columns, or Windows-1252 encoding — causes the entire import to fail with no clear error message. Profiles successfully added to the Suppression List are removed from all active Lists & Segments automatically.

How to diagnose the failure:

1. Open your suppression file in a plain text editor (not Excel)
2. Check the first line — it must be exactly email with no extra characters
3. Check for a BOM marker at the very start of the file (appears as  or similar in a text editor)
4. Confirm the file extension is .csv and not .xlsx or .txt

Fix steps:

1. Export your Suppression List as CSV from your source system
2. Open in Google Sheets or a text editor and verify the header is exactly email
3. Remove any additional columns — Suppression List imports only accept the email column
4. Save as UTF-8 without BOM (in Excel: Save As → CSV UTF-8 (comma delimited))
5. For files showing BOM characters, re-save as UTF-8 without BOM, or use Data Cleaner to strip the BOM automatically

[Screenshot: Text editor view showing clean Suppression List format with single email column]

The BOM problem: Windows Excel saves CSV files with a UTF-8 BOM by default. Klaviyo's Suppression List importer rejects BOM-prefixed files. If you're on Windows and generating suppression exports from Excel, always verify and strip the BOM before importing.

Edge case — Source property on imported Profiles:

The Source property is not documented as required in Klaviyo's CSV template but behaves as if it is. Profiles imported without a Source value are flagged as low-quality and may be deprioritized in deliverability scoring. Always include a Source column in your profile import CSVs (e.g., "Manual Import 2026-05", "Onboarding Form"). This applies to profile imports — Suppression List imports use only the email column, so Source does not apply there.

For a full explanation of BOM and encoding issues in CSV files, see our complete guide to fixing CSV encoding issues.

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Error 4: Duplicate Profiles

Klaviyo's "Profile already exists with conflicting data" detection fires when an email address in your import already exists as a Profile in your Klaviyo account. Unlike platforms that silently merge duplicates, Klaviyo surfaces the conflict and lets you choose how to handle it during the import setup. The Profile's existing Profile Properties are preserved unless your CSV explicitly overwrites them.

This is most common when re-importing after a partial failure (a "List import partially complete with X errors" result), updating Profile Properties on existing Profiles, or migrating from another email platform where some Profiles were already manually added to Klaviyo.

Understanding Klaviyo's duplicate handling options:

During import setup, Klaviyo gives you two choices for duplicates:

• Update existing profiles — merges the imported data with the existing Profile's Profile Properties, keeping existing fields unless your CSV overwrites them; use this when syncing updated data from a CRM export
• Skip duplicates — imports only net-new Profiles, leaving existing records unchanged; use this when you only want to Subscribe to lists rather than update Profile Properties

Fix steps:

1. Before importing, decide whether you want to update existing Profile Properties or import only new Profiles
2. Set the duplicate handling option in Klaviyo's import wizard before uploading
3. For large lists where you want to import only net-new Profiles, deduplicate your CSV against your existing Klaviyo export first — export from Lists & Segments → your list → Export
4. Use SplitForge Data Cleaner to remove duplicate emails from your CSV before import — it catches duplicates within the file itself as well as supporting deduplication against a reference list

[Screenshot: Klaviyo import settings showing duplicate handling options]

Before large imports: Export your current Klaviyo Profiles from Lists & Segments, then deduplicate your import file against that export using email as the match key. This eliminates duplicates before they hit Klaviyo's validator and makes the import summary cleaner to audit. For a full deduplication workflow, see our guide to removing duplicate emails before CRM import.

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Consent-First Batch Preparation for Klaviyo Import

Klaviyo's import validation is consent-aware — a CSV that passes field formatting checks can still fail silently if consent columns are malformed or mismatched. Before any bulk fix pass, audit consent fields first.

Consent column audit checklist:

1. Confirm $email_consent and $sms_consent are separate boolean columns (true/false) — never map a single consent flag to both; doing so silently overwrites whichever consent state was previously recorded
2. If $sms_consent is present, $sms_consent_timestamp must also be present with ISO 8601 + timezone offset (e.g., 2026-01-15T10:30:00-05:00)
3. If $email_consent is present, $email_consent_timestamp must also be present in the same format
4. Confirm the Source column is populated — Profiles without Source are scored as low-quality in Klaviyo's deliverability ranking
5. Cross-reference your import file against your existing Klaviyo Suppression List: go to Lists & Segments → Suppressions → Export and remove any email addresses that already appear there

Batch fix workflow:

1. Download the import error report from Klaviyo's import results screen
2. Run your CSV through SplitForge Data Cleaner — it flags phone formatting violations, BOM encoding artifacts, column name mismatches against Klaviyo's Profile property schema, and duplicate emails within the file
3. Fix all flagged issues in a single pass
4. Re-check the consent column structure against the checklist above before re-uploading
5. Re-import to the correct List in Lists & Segments

This resolves most Klaviyo import failures in under ten minutes for files up to 100,000 rows. For a broader overview of CSV import errors across all platforms, see our complete CSV import errors guide.

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Additional Resources

Official Klaviyo Documentation:

• Klaviyo Guide to Importing a List or Segment — Official CSV import field requirements and column naming
• Klaviyo's CSV import documentation — Complete field reference including $consent, $email_consent_timestamp, $sms_consent_timestamp, and Source property requirements
• Klaviyo Suppression List Import Guide — Suppression file format requirements
• Klaviyo Profile API spec — Full Profile Properties schema showing all system-reserved fields and their expected formats

Compliance Standards:

• ITU-T E.164: International Phone Number Standard — The phone format Klaviyo's validator requires
• RFC 4180: CSV Format Specification — Official CSV structure standard
• Unicode BOM Specification — Why BOM characters cause import failures

Tested: Klaviyo profile import and suppression list import modules, Chrome 122, Windows 11. March 2026.

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FAQ