I think that's problem, because back then i was trying all different combinations of versions of magisk and versions of VoIP recorder app till i found proper combination that worked for my device (LG V30 Oreo), if you're interested, you can read more about it here, but back then there wasn't warning message about "need to update", so version 1.7 worked for me, but i'm rn using 1.2 with magisk 20.4:
Android VoIP Call Recording - Record video calls and voice calls from VoIP apps such as WhatsApp, Viber, Facebook Messenger, Google Voice, Google Hangouts, Google Duo, Line, WeChat, Skype, magicApp, Signal etc, is a feature many Android users are...
You should try reinstalling/rerooting more versions of magisks on phone and find which one works with VoIP recorder 1.2, or even better with this pro mod unlocked version 2.0 if it doesn't have "update" warning and if it works on your device (sadly on my device any newer version than 1.7 doesn't work for some reason no matter "update" message and no matter version of magisk i install) :
VoIP Recorder & Screen Recorde Mod: 100% working on 405 devices, voted by 32, developed by boldbeast-software-inc. Pro..
It could also be Android version problem if you have 12, as i think for that one app isn't supported?