I have bought unlocker.
But times have changed and now I am using Android without google apps and google account.
So unlocker does not work anymore and I am forced to use free version.
I’d be happy to pay again if there is a way to use Pro version without google account (AOSP without google apps).
I am using Yatse almost daily for years now. So I do not mind buying it again. Of course buying process should also be google free (paypal is fine).
Yatse™ - Troubleshooting Yatse payment issues there’s paypal license tied to an email account that you need to declare at OS level. (IMAP account with disabled sync is fine)
Splitted to avoid spam.
Do you mean using GMAIL app? That is also google and requires google services to be installed.
I use K9-mail and that does not register any accounts on OS level. And I do not see why it should.
But I get your point.
I’ll dig around a bit to see if I can make email account appear somehow on OS level.
I mean any email. And Yatse have no way to check accounts defined in all the random mail apps.
So only OS accounts are supported and no there’s no need for any Play Services this unlocker was made for that use case.
The question was about gmail app not about gmail account.
Gmail app might register account on OS level.
I have just tried few open source email clients but so far none of them register account on OS level. I really do not see any good reason why email client should do that.
This is not about email clients, this is about you going to Android settings then account then adding an account with the email you register the unlocker too.
Quite a few people did manage to use that unlocker 
Any tips?
If I choose Add Account (+ button) there is nothing to choose from, except some apps that do register accounts on OS level but those are not email accounts. Like owncloud.
There is nothing to choose that allows adding an email account.
On devices with Google apps you can choose “Google” and add google account. But I do not have any Google stuff anymore.
Without google means no google stuff at all. No “google play services”, no google email stuff, nothing.
I use mostly F-Droid for apps and Aurora Store with anonymous login for some things from Google Play, like Yatse.
It does not mean Android with few apps removed or not logged into google account. It means AOSP-like ROM without gapps package.
I checked a device with Google apps. Yes, if Gmail app is installed/enabled then you have “Mail (IMAP)” available under “Add Account”.
But I do not have even google framework/services. Without that it is not even possible to install Gmail app.
That is what AOSP is all about. And also ROMs based on that, like LineageOS. There is no google apps/services/frameworks. Unless you choose to add it. But that is the whole point of AOSP - it’s without all google stuff.
Well I don’t know what your ROM is missing but I do know that all the users who do not want to use Google do use this unlocker with success on Lineage and others so are able to add an account in Android settings probably added via the default email application those embed.
It’s been a really long time since I played with custom ROMS and it’s out of Yatse support scope, but I do not have other solutions to propose sorry.
Installation procedure is the same with most custom roms:
And if that optional gapps (google framework, services and selection of google apps) is not installed and gmail app is not installed then there is no “Mail (IMAP)” selection under Add Account.
And I do not have gapps. I want to have google free device.
I know that you seems to know better and can’t consider that anything I say might be true 
But as said AOSP platform/packages/apps/Email - Git at Google have a default email client that support imap / pop accounts at OS level.
Since this is a conversation that goes nowhere as I do not need a lecture about AOSP and you know better I’ll close this issue as there’s nothing more I can tell you.