Development team has reached maximum number of registered iPhone devices

Contacted the Apple Developer Program Support who solved it by deleting the old devices associated to the old membership.

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.