Reseller checkout fails with 'lastName must not be empty'
Reseller checkout for domains and site bundles can fail with the error Could not complete order: API error (400): lastName must not be empty when the signed-in user's Eventually profile has no last name. The app now falls back to the registrant contact's last name from the checkout form to prevent this failure.
When this error appears
This error occurs during the reseller purchase flow for a domain or site-and-domain bundle, on the step before payment is processed. It happens when the signed-in user's Eventually profile has a blank last name, for example because the account was created with a single-word name.
Both purchase paths are affected because they share the same customer provisioning step:
Domain-only purchases from Settings → Domains → Buy a domain
Site-and-domain bundle purchases from Settings → Sites → Build a site
This failure occurs before any charge is captured, so there is no payment risk and no order is created.
Why the error happens
Reseller purchases create a Squarespace customer record using the signed-in user's Eventually profile name. Squarespace requires a non-empty last name for customer provisioning. If the user signed up with a single-word name (for example, only a first name), the profile last name is blank, and Squarespace rejects the request with a 400 error.
The checkout form itself requires a last name in the registrant contact section, but the provisioning step was using the profile name rather than the form value.
How the fix works
Customer provisioning now uses the signed-in user's profile last name when it is present. If the profile last name is blank, it falls back to the registrant contact's last name from the checkout form.
If your Eventually profile has a last name, that value is used for customer provisioning.
If your profile last name is blank, the app uses the last name you entered in the registrant contact form instead.
The registrant last name in the checkout form remains required.
What to do if you still see the error
If the error still appears after this fix:
Confirm that the Last name field in the registrant contact form is filled in.
Check that your Eventually profile has a last name saved. Go to your account settings and update your profile if needed.
Contact Eventually support with the exact error text and the page you were on (Domains or Sites).
Related guides
Add a new card during reseller checkout — Walk through the reseller purchase steps
Reseller checkout shows $0.00 or missing domains — Troubleshoot empty cart and missing domain rows on the Confirm step
Choose a domain registration term — How the term selector and total work on the Confirm step
Updating your profile, email, and password — How to update your account profile information