IT help needed

The routers wifi loses internet, that is all. The AP is an access point, not a router. Network goes modem > router > switch > AP. It should be pretty simple to connect right? Just plug it inti ghe network. I got the AP working fine but the router in a separate office loses its wifi internet (but hardlines work)

AP is not a DHCP server, router is an old Netgear with factory settings except for SSID and password. AP also has factory settings