From your diagram, AP3 is the root bridge because it is connected to ISP, so AP2 will be a repeater, but 1242 can't work both as repeater and AP. So the diagram won't work. you have 3 alternative options:
1. not let AP2 to connect wireless clients, only configure AP2 as a repeater.
2. If AP1 can connect to AP3 directly, then configure AP3 as root-bridge with wireless clients, configure both AP1 and AP2 as non-root bridge withe wireless clients.
3. If AP1 can't connect to AP3 directly, you need to add an additional AP4 to have back-to-back connection with AP2, configure AP1 and AP4 as non-root bridge with wireless clients, configure AP2 and AP3 as root-bridge with wireless clients; ap1 peered with AP2, AP4 peered with AP3, AP2 and AP4 are interconnected by ethernet port.