Account not eligible to link to xbox for 2k21

you are to young, 2k checks the date of birth from you xbox account and double checks when creating an mplayer account.

minimum age is required.

I'm pretty sure you need to have your Microsoft/Xbox account linked with your Mixer account to be eligable.

Was your Microsoft/Xbox account linked to your Mixer account at the time or not?

Also were watching the stream live, or the VOD, you need to watch live to be eligable.

Xbox on my TV

I already have 2K21 active

if you go to the link provided and sign in with the same account as your Xbox it will show you the enforcement actions against you and if your case is eligible there will be a button for submitting a case review.

if your ban is only for a day then it won't be eligible

Sorry to hear it. The dashboard ad you saw would have led to the page I linked I my post before to check if you are eligible or not. Unfortunately if the page states your account is not eligible for the referral promotion, we are unable to assist further.
Eligibility is based on if your a Game Pass/Gold subscriber, but eligibility also depends on whether or not you have friends on your Xbox Live friends list who are eligible to receive the referral.

Hope this helps clear up the issue!