How to fix a Klaviyo CSV before import

A failed import is often a formatting problem rather than a data problem. The fastest workflow is to validate identifiers, consent fields, property types and row structure before uploading again.

1. Put a profile identifier first

Klaviyo recommends using Email or Phone Number as the first column of a list import. ReadyRows recognizes common aliases such as email_address and can move the identifier column to the front automatically.

2. Keep the CSV within the upload limit

Klaviyo currently documents a 50 MB maximum for CSV list uploads. Larger exports should be split before import. ReadyRows flags files above that limit.

3. Treat consent as data you must not guess

If you include consent columns, values need to match the consent states Klaviyo accepts. ReadyRows validates and normalizes obvious spelling/casing variants, but it never marks a person as subscribed when the source data does not say so.

4. Match custom properties to the right type

Klaviyo supports text, numeric, Boolean, date and list-style properties during mapping. A list value should be a JSON array such as ["red","blue"]. Numeric values should not include currency symbols. ReadyRows samples each column and recommends a mapping type.

5. Separate blockers instead of deleting rows

A safer cleanup process keeps the original data. ReadyRows exports blocked rows separately with a rejection reason, while the import-ready file contains only rows that passed blocking checks.

Official reference

Rules summarized here are based on Klaviyo Help Center guidance for importing subscribers and troubleshooting invalid formats: import subscribers to a list and invalid format errors.

ReadyRows is an independent tool and is not affiliated with Klaviyo. Product rules can change; for account-specific decisions, confirm the latest guidance in Klaviyo's Help Center.