How do I fix error code 0x80070015?

I performed all the steps in order and all the commands seemed to be executed smoothly. I used wsreset, closed the store and restarted my pc. It took about an hour to restart, since it told me it was updating my pc. When it finally finished, I tried again, but it still didn't work.

I am very sorry for the late response, but I have been away from my computer and unable to try this command. I tried the command, but It gave me this error.

Copy and paste the following command into the Powershell window and hit Enter:

powershell -ExecutionPolicy Unrestricted Add-AppxPackage -DisableDevelopmentMode -Register $Env:SystemRoot\WinStore\AppxManifest.XML

Unfortunately it was not possible to execute the commands correctly.

Please perform this procedure. All of these steps may take some time to execute, just be patient.

1. Press the Windows + X keys and select Command Prompt (Administrator) or Windows PowerShell (Administrator).

2. In the window that will open, copy and paste the command sfc /scannow and press Enter.

3. When finished, type the command DISM.exe /Online /Cleanup-image /Scanhealth and press Enter.

4. After the above, perform the same process with DISM.exe /Online /Cleanup-image /Restorehealth.

5. In the Windows browser type wsreset and execute (this will open the Microsoft store, close it).

When finished, restart the PC and test.

Thank you for the response, my external hard drive has the NTFS file system and I used both of the commands on PowerShell as administrator and restarted, but it still shows the same error. This picture is what it looked like after I ran (Get-AppXPackage -AllUsers | Foreach {Add-AppXPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}) and I'm not sure whether It's supposed to look like that.