"We are unable to proceed with the request due to account eligibility reasons"

We have a brand registered with Amazon Brand Registry - but every time we try to link the Brand we have registered, to our selling account on Amazon we keep getting this message - "We are unable to proceed with the request due to account eligibility reasons" We have opened multiple help cases with Amazon Brand Registry support but despite going back and forth multiple times nobody can give us any information on how we resolve the reason our account is not eligible. Our account health is good in all Amazon countries we sell in. Support advises us to try on different browsers and different days but this doesnt make any difference, which seems to be obvious. Can anybody help advise how we solve this issue?