Google Play Store no longer accessible; Email app also suddenly dead

[Lord Vader]

I posted this in the HTC 10 section, so I'm not sure if that's correct or if this section is, since I'm on Adroid Nugat.

I'm running a 6-month-old HTC 10, unrooted. I've faithfully used Mail Droid Pro as my Email app, never having experienced a problem. Until tonight. About an hour ago when I went to check an Email I was expecting, I saw on the bottom of the screen this never before seen message:

License is expired or can't be found.

BUY CHECK LICENSE

Now, I bought the Pro version of this Email app, so there is no further license to have to "buy." Regardless, I pressed the "check license" button and absolutely nothing happened. So then I pressed the "buy" button, and the app redirects to what is supposed to be the Google Play Store app. However, all that comes up is a totally blank, white screen, with which I can do nothing. I can get back to my home screen, and when I go to my app drawer and try to access the Play store that way, the same thing happens--I get a totally blank, white screen. No matter what I do--phone reset, etc.--I cannot in any way get the Play Store to open or Mail Droid Pro to do anything.

Any thoughts?