Error code (0x80070102) when trying to open Undertale through Xbox App

May I know what did you tried so far to fix this?
In that way I can advise you different things or how to proceed

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this Markus

We can try to isolate the problem a bit more, but first try and double check this:

Open Settings, click Update and Security and then Windows Update
Click Check for Updates

Click the Download and Install Now option, if available (Install optional updates as well)

Also, check the Microsoft Store for any updates on the Xbox apps and its services and update everything too. (Click on get updates)

Now, sign out from your account on both Xbox app and Microsoft Store and do this:

Go to windows settings > apps > search for gaming services app > click on it and select advanced options.

After that, click repair and then reset

Then do the same for the Xbox and Undertale app:

Go to windows settings > apps > search for Xbox app > click on it and select advanced options.

After that, click repair and then reset

Finally do this:

Step 1: Open the Run window by pressing Windows + R key.

Step 2: Input WSReset.exe in the Run window and click OK.

Step 3: Then a command prompt window will appear. After a few seconds, Windows Store will open.

Sign in again on both Microsoft store and Xbox app with your account and try again

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If the issue try and double check this:
Press Windows button and type Services

On Services App from the list of results, press right-click and run it as administrator

Scroll to the bottom and find the following services:

IP Helper
Xbox Live Auth Manager
Xbox Live Game Save
Xbox Live Networking Service
Gaming Services

And do this with each of the services listed above:

Right-click over the service and select Properties.
Find the Startup type section and make sure it’s set to Automatic (if not, change it to automatic)
If the service isn’t started, click Start to start the services

Restart your PC and try again

I restarted my computer and opened the Xbox app, but no notification, blue or other colors, appeared.

This can be a bit odd, but do you have the game installed on a different drive than C:?
If yes, please try moving the game to the C: drive and try again

If that doesn't work try this:

A. Reinstall Gaming Services using powershell command

Press Windows key + X and then select Windows PowerShell (Admin).

Type or copy / past the following command and press Enter:

Get-AppxPackage *gamingservices* -allusers | remove-appxpackage -allusers

Restart the PC and Open the Xbox application.

A blue notification with the following message is going to appear at the bottom:
"This app needs an extra component. Gaming Services is needed for playing some games. Administrator approval required. Install"

Select Install to reinstall Gaming Services, once installed check again

B. Open task manager > select the startup tab > disable all the programs listed there temporarily
Restart the PC and try again

C. Do a clean boot in your PC and try again
https://support.microsoft.com/en-us/windows/cre...

Sadly this did not fix my problem, also the computer did not allow me to restart Xbox so I could only repair it.