I’m getting a “user does not exist” when I use the one-click login, how do I solve this?

If you encounter a "user not found" error when using the one-click login functionality, you should check the following:

Plugin Version Consistency: Ensure that the Host Plugin on your storefront and the Client plugin on your production version of your client application have the latest version. Remember to deploy after any updates.
Custom User Role Existence: If you're using a custom user role, verify that the role exists on the production version of your client application. Make sure to use the slug of the role rather than the name. For example: site-owner instead of Site Owner
Unique Email Addresses: Make sure that the user created during the tenant provisioning has a different email address than any existing users on the production Version of your client application. You might consider using a temporary email service like tempmail.com for testing purposes.
Tenant Provisioning Check: If the above steps don't resolve the issue, create a tenant, wait for it to provision, and then log in through the Console. Check the user tab for a user with the name "firstname_lastname" that matches the data and email used during checkout. If the user isn't there, your tenant might be encountering provisioning errors.

If you've gone through these checks and the problem persists, it may be due to a known issue or another problem with the provisioning of your tenants. In such cases, it's advisable to contact support for further assistance.