Is there any software that can be used as a WiFi billing software for hotels, coffee shops, etc that is (hardware) manufacturer agnostic? Preferrably something based around RADIUS?
Dont know about your hwardware but there is a full flag radius server billing system based on WHMCS which is used by many ISPs’
https://marketplace.whmcs.com/product/6861-freeradius-module-for-whmcs
This module is perfectly works with radius server and Mioritk routers, check if it suits your requirements.