The Certification Authority Browser Forum (CA/B) has recently passed ballot SC45 related to file-based domain validation, also known as HTTP File Upload at ZeroSSL.
Starting from the November 22nd, 2021, you will not be able to use HTTP File Upload as a validation method for wildcard certificates. Instead, you need to use CNAME (DNS) or E-mail validation.
The change was created in response to the concern that File-Based validation is not a strong enough way to demonstrate that someone has control over a domain's entire namespace.