As the error message says: disc-lite5 already serves maximum number of clients and the new one is not allowed to connect.
Two things, in order from less important to the critical one:
- taking from description from diagram "PTP BRIDGE AP" ... I'm assuming that disc-lite5 is running in "bridge" mode ... which can only serve single station. You would have to change it to "AP-bridge".
Alas you probably can't, see next bullet.
- disc-lite5 comes with ROS license level 3 ... looking at ROS license levels one can see "Wireless AP mode (PtMP): No". For PtMP (which is what you're trying to build with two stations connecting to same "AP") you'd need at least license level 4.
You'll have to contact official Mikrotik reseller for pricing (there are on-line ones as well) for pricing, but I heard they don't come cheap. So it might be better for you to replace disc-lite5 with a device which comes with license level 4 by default (product page does state this information)