Can't sync Android Notes app to Nextcloud

Nextcloud version (eg, 12.0.2): 17.0.3
Operating system and version (eg, Ubuntu 17.04): Ubuntu 18.04.4

The issue you are facing:

Yesterday my Notes app stopped syncing with Nextcloud.

Can anyone help troubleshoot this?

Here’s what happens when I try to get the Android Notes app to sync with my NC instance:

App Version: 2.10.3
App Version Code: 81
Files App Version Code: 30100190

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OS Version: 4.14.111-gb7713fd5d6ed-ab5820689(5831595)
OS API Level: 29
Device: flame
Model (and Product): Pixel 4 (flame)

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com.nextcloud.android.sso.exceptions.TokenMismatchException: Provided authentication token does not match or package name is not permitted to perform this action
	at com.nextcloud.android.sso.api.AidlNetworkRequest.performNetworkRequestV2(AidlNetworkRequest.java:172)
	at com.nextcloud.android.sso.api.NextcloudAPI.performNetworkRequestV2(NextcloudAPI.java:148)
	at it.niedermann.owncloud.notes.persistence.NotesClient.requestServer(NotesClient.java:163)
	at it.niedermann.owncloud.notes.persistence.NotesClient.getNotes(NotesClient.java:98)
	at it.niedermann.owncloud.notes.persistence.NoteServerSyncHelper$SyncTask.pullRemoteChanges(NoteServerSyncHelper.java:413)
	at it.niedermann.owncloud.notes.persistence.NoteServerSyncHelper$SyncTask.doInBackground(NoteServerSyncHelper.java:320)
	at it.niedermann.owncloud.notes.persistence.NoteServerSyncHelper$SyncTask.doInBackground(NoteServerSyncHelper.java:284)
	at android.os.AsyncTask$3.call(AsyncTask.java:378)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:289)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:919)

See https://github.com/stefan-niedermann/nextcloud-notes/issues/763

You need to clear the Notes app storage (at least it worked for me). Beware, unsync’ed notes will be lost.