Just insure NOTHING is plugged into any of the LAN ports of the "REMOTE AP ROUTER" except the 8508T switch.
The "REMOTE AP ROUTER" should be set to "AP MODE" or if no such option available, then DHCP disabled and given a unique static IP in the same subnet as the "MAIN ROUTER" but outside the DHCP pool of the "MAIN ROUTER"; then the "REMOTE AP ROUTER" should be connected to the 8508T switch via one of its LAN ports.
Just insure NOTHING is plugged into any of the LAN ports of the "REMOTE AP ROUTER" except the 8508T switch.
The "REMOTE AP ROUTER" should be set to "AP MODE" or if no such option available, then DHCP disabled and given a unique static IP in the same subnet as the "MAIN ROUTER" but outside the DHCP pool of the "MAIN ROUTER"; then the "REMOTE AP ROUTER" should be connected to the 8508T switch via one of its LAN ports.