Apple Account 2-Factor Authentication Problem

ep_505 wrote:

If it helps, the iPhone that my phone number is on has another different apple account on it (my family member’s account), but the 2fa should be on his phone number, so I don’t know if it is related to that?

This is almost certainly the explanation.

Have you previously established this iPhone number as a trusted phone number on your Apple Account?

About trusted phone numbers and trusted devices for Apple Account - Apple Support

It sounds like the answer is ‘No.”

I cannot personally tell you how to proceed, as I personally know nothing about setting up an Apple Account using a method not involving an Apple device.

For a generic, numeric, unknown "error”, or simply unhelpful messages, I suggest you contact Apple.

Refer to this page for Apple Support features ➔ Contact - Official Apple Support

Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page under “Get more help” (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.

This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple Support - Apple Support For some countries look under “Other” listing at the end of the list. Not every country has telephone support, and phone numbers may only work when calling from the same country.