I don’t see there is a problem. But too many configurations is made so need to test.

Maybe you don’t need to use relayd. Why don’t just use your Pi to connect to your main router directly via wireless? In the new version of PI there is wifi already. In older versions you can just install a small USB dongle. It is quite easy and quick without complex configurations.

Can your tablet connect to the Pi when it is connected to MT300A?