Check that Stripe Email Airtable Field (Optional) points to the customer's email address. If it is stored in a linked record, add a field in Airtable to lookup the linked record's "Email" field and select that lookup field. Ensure the lookup returns one email address, not multiple addresses. Lookup values are converted to text before being sent to Stripe; a linked-record ID is not an email address.
I'm getting an error that the email field is invalid before loading the Stripe Checkout page
Unknown error code: email_invalid.