Error 924 
Is there a website link to get the app from? I’ve tried with and without a VPN from within Mainland China.
Do you use a Chinese mobile? Or do you use one purchased outside of China?
If you have a functioning VPN and a foreign mobile, there should be no problems. If your mobile is purchased in China, you’ll have to install the apk for google play and google play service. But you probably downloaded apps from play store before, right?
I bought the phone in Shanghai, they installed Google Play Store and I use Astrill which works most of the time. I’ll try a few different channels and see if that helps. Do you have a direct link to your apk?
Yes, I download most apps from the playstore; although one of them I had to install directly from a app-provider’s website; I think it was zizzle.io
That’s quite the service 
I did all these things by myself
This is the link to the apk here. But if you can download other apps, normally there shouldn’t be a problem
OK, I googled error 924. The internet says that one should clean the app cache. I’d clean both, the app for google play as well as google play services.