Well well, I logged into my Adguard account in the app, and it activated and said "valid until the end of time", which made me almost drop my phone! So this can be deleted now. I'm super happy!!! Thank you so much!If push comes to shove, you could purchase a cheap lifetime license from StackSocial and use that - you can still continue beta testing with normal licenses by using the beta or nightly update channel.
StackSocial AdGuard Personal (3 devices) lifetime license: https://stacksocial.com/sales/adguard-personal-plan-lifetime-subscription
StackSocial AdGuard Family (9 devices) lifetime license: https://stacksocial.com/sales/adguard-family-plan-lifetime-subscription
To be frank though (and this is my personal opinion), I wouldn't be surprised if the beta testing program which offers a beta testing license goes away at some point in the future. It was created at a time when there was a need for a testing team to test releases before they were released to the stable channel. Which honestly is not needed these days anymore as anyone can beta test AdGuard apps due to the addition of the beta and nightly update channels with no special beta tester license needed.