I'm a new freelancer and have big experience in mikrotik routers, routing, VLAN, VPN, HotSpot, Linux System Admin, cloud services. I manage about 100 mikrotik routers. I have project like your. AP on bus stations connected to mikrotik router with usermanager and hotspot module. When client connect to AP is automatic redirected to captival PHP portal with ADS, mikrotik router detect client MAC address, if client is new open registration form with name, email and phone. When client register, system send SMS with PIN code to verify phone number and redirect to free internet with bandwidth limit for every client. After 15 minutes, internet is disconnected and client is redirected to captival portal to see ADS again and click on 1-2 buttons to add 15 minutes. If client is already register by MAC address of device go to captival portal to see some ADS and click 1-2 buttons to open session for 15 minutes.
I'm not so good PHP developer, but I can edit PHP web page to communicate with mikrotik router and execute command on it.