What the docs say:
Official docs (AB Tasty, Variation API error codes): the real error codes when managing variations through the API. InvalidPayload means the variation data missed required fields or had invalid values. ParentNotFound means the parent campaign ID is invalid. PermissionDenied means the user cannot create or modify variations in that campaign. DuplicateRef means a variation with the same reference already exists in the campaign. InvalidDependency means a related resource is missing or not accessible.

What works:
When the AB Tasty Variation API errors: InvalidPayload means re-check required fields in your request body. ParentNotFound means the campaign ID is wrong or the campaign was deleted. PermissionDenied is an access problem, not a data problem, check the user's campaign permissions. DuplicateRef means you already created that variation reference, fetch it instead of recreating. InvalidDependency means create or fix the parent resource first.