The domain troubleshooting guide can help with most custom domain configuration issues. You might be able to use that guide to solve it before a human is available to help you. Then you can come back here and share the answer for bonus points.
You can also use v0 to narrow down the possibilities.
This was intentional given that 308 is the correct status code to use nowadays, see the documentation: 308 Permanent Redirect - HTTP | MDN. 301 has some flaws like form data not going through.