I believe this is a problem with paid developer accounts that have expired and become free developer accounts. Technically free accounts are limited to 3 devices. If you have a previous paid account that had more than 3, I bet Apple didn’t clear out those devices, which means you are over your limit of devices. Other are experiencing the issue here.
I think your best move would be to sign up for a new, free account, or pay to restore your access to the full 100 device limit for a paid individual account.