Using captive portals for paid access to wifi: Should I roll my own?

I am creating an open source project so any "entrepreneur" can identify area with a lack of WIFI connectivity, and install a self contained Access Point portal accepting Bitcoin payment for other WIFI consumer to get access to internet. (The payment part being also self-contained without intermediary or third party services)

It will basically a "Box" bundling PC Engines apu4c4 running on OpenWRT and a Raspberry PI handling the payment portal. (Based on the BTCPayServer project,which is an open source payment processor that I maintain) The apu4c4 have a wifi module to create the AP, and a SIM Card module to get 4G connectivity.

I managed to get my apu4c4 flashed with OpenWRT. Now it seems I need to figure out how to install a captive portal. There seems to be lot's of choice.

But on those choices: 1. Nodogsplash doc is outdated 2. CoovaChili has almost no doc 3. WifiDog doc has lot's of broken links and images and hole in the docs

It seems to me all those projects are severely unmaintained. So I am now wondering if I should not create my own captive portal rather than trying to use those projects?

For those who used it, it seems that the captive portal, are using a RADIUS server for some of their function. What is the goal of a RADIUS server? I understood that the AP send accounting data to the RADIUS. But I does the RADIUS server is able to tell the AP to stop internet the connectivity for a specific MAC address if such MAC address did not paid?

No matter how much documentation and video I am reading on the subject, the relation between RADIUS, Captive Portals and what happen on OpenWRT are not clear.

So to summarize my questions:

1. Wifidog, CoovaChili, Nodogsplash or custom solution?
2. What is the relation between a captive portal software, open wrt and a RADIUS server?