So you are about to set your 2FA, and the mobile number hasn't been accepted? These aren't serious issues, so there's no need to panic. I assume you are using an incorrect format for your mobile number. Because likely they are asking for the international format of your mobile number. If you don't have privacy issues, you may share your country. So other users would help you with the correct format.

However, since you posted here, I believe the BC game support team would solve it. Try to reach them through support, so they might help you as well. Don't worry; the problem can be solved.