I just tried to purchase a full license of Poweramp, and got an email back from the payment processing company saying that they cannot accept my purchase since their system does not accept my email domain (tutanota.com). This is my main, permanent email address, and while I've had similar issues where the domain isn't in a company's system since they've never heard of it, I have never had anyone recognize the domain and reject it. Follow this link to see an image of the message I received from the payment processor: https://imgur.com/a/ocb0T48
You have a quality product, and I want to buy it, but I'm not going to get a different email address to do it.