Again, Force/31 cannot help me because it does not allow me to type in my own gateway and subnet, such as 166.xxx.yyy.1 and 255.255.255.0. Force/31 still chooses the gateway and subnet for me.
Below is a diagram. I believe the reason I cannot communicate between the routers is that the WAN IP address on the other router just happens to be the same as the WAN gateway on the Pepwave router. There is a conflict. I cannot change the WAN IP addresses, but I should be able to change the gateway and subnet mask.
Perhaps I should start a new thread for this issue because the Subnet Selection Mode and Force/31 are not solutions.