After I purchased Cryptomator for Android, I created a new connection to my hosting provider. My cloud space at this provider can be reached via Webdav.
Hence, I selected the Webdav protocoll in Cryptomator, and established successfully a connection to my cloud space.
After that, I successfully created a vault inside my cloud space. I then opened my new vault, after entering the vault’s password. So far, so good.
In my new vault, I tried to create a text file (by using Cryptomator’s function), which worked without any issues.
So all this proves that my connection to the could space works, as well as creating files inside my new vault.
The problem now is when I try to upload a file by using the upload function in the Cryptomator app. After I select a file to upload, the error message “authentication failed” appears. This is also shown in the debug log file created by the app.
Occassionally, I also receive the error message “server not found”.
All of this doesn’t make any sense, since I am connected to the cloud space and also successfully unlocked the vault.
Initially I received a message from Support, sent them the debug log file, tested Cryptomator also on Windows and Linux (both successfully), but it still keeps failing on Android. There seems to be no solution.
For sure, you’ll get a refund!
You can follow the google play store instructions in order to obtain a refund Learn about refunds on Google Play - Google Play Help or you send me in a private message your google mail of the purchase.
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I’m running sometimes also into this issue 
… but AFWall+ is awesome 