I am a long time Enpass user and just installed LineageOS on my phone and want to reduce the use of gApps on my system. Because of that I am now using microG with Yalp store to access the Play Store.
After installing my most important apps I am now facing a big problem. Due to the fact that the pro version of the Enpass application is only buyable through in app purchasement I am not able to really use it, because it requires gApps.
I have found a thread of another person with the same problem here, but you didn't seem to get his problem.
The solution would be to do it like Nova launcher or other popular apps. Distribute two apps. One free and one pro.
This is I cannot use your application anymore.