Access point not working after been moved to differnt location

Hi team, 

I need your help urgently.

Scenario:

We have 5 sites across the business. "Site A" has all the servers, DC, Backup etc and has a Draytek Firewall and Cisco AP's.

"Site B" which is the flagship store has Fortigate all throughout. ( Firewall, an access point etc)

Site C, D, E is similar to "site A" different devices.

We had issues with wireless connectivity at "Site A" a few days ago. Wifi is not strong enough.

So I decided to take one of the Fortinet AP in "Site B" and placed it in "Site A". I waited for nearly an hour. The Fortinet AP wasn't showing in the controller on "site B" even though it is lit up. 

Am I doing something wrong?

Regards, Networking