Please note the AP ID may change (to re use some ID's) if there's Reindexing of DB at time of upgrade (not all upgrades) or done at time of any Airwave triubleshooting. MAC Address is better option for such use cases. However, here's the option to get AP ID's.
ap_list.xml, which can be used as API or from UI https://<Airwave IP>/ap_list.xml will list the AP details including AP ID's