It can sometimes happen that an app suddenly shows problems when you download it from the Microsoft Store. Anything could be going on, of course. These are the things you can do anyway to fix the problem. In any case, it helps to restart your device or to ensure that you have the most recent version of Windows 10 on your PC.
If you did that and it still doesn't work, it's best to log in and out of the Microsoft Store. At the top right is your profile picture. Tap on that and tap Log Out in the next window. Now press the button at the top right again and log in again with your Microsoft account.
A second option is to clear the cache of the Microsoft Store. To do this, open the Command Prompt. Now type in the command wsreset and press Enter. Follow the steps on the screen and the problem should be solved.
Microsoft Store: The Troubleshooter
Do the above options not help? Then we have the troubleshooter for the Microsoft Store. Go to Settings / Update & Security / Troubleshooting. Under the heading Detect and fix other issues, it says Windows Store apps at the bottom. Press that and hit the Run Troubleshooter button. Follow the steps on the screen again.
The fourth option is to reset the Microsoft Store. Go to Settings / Apps / Apps & Features. In the middle is somewhere Microsoft Store. Click on that and open the advanced settings. Near the bottom, still above Delete, is the Reset option. This will reset the app. Follow the steps on the screen again.
PowerShell can offer a solution
If nothing really works, you can still uninstall and reinstall the Microsoft Store. To do that, open PowerShell (open Start and type PowerShell, select the program). You have to run it as administrator. Type the following line: Get-AppxPackage Microsoft.WindowsStore | Remove-AppxPackage.
After that you have to take over and then press Enter. Add-AppxPackage -register "C:\Program Files\WindowsApps\Microsoft.WindowsStore*\AppxManifest.xml" -DisableDevelopmentMode.
If you now follow the steps again, the Store will be reinstalled and the problems should really be solved. If this doesn't work either, you can still check whether the download works with a new or different profile or account. The last resort is to factory reset your entire device, but that's probably not what you want.