Symptoms
Error while setting up email notifications for scheduled execution packages. Error Message received:
Error: One or more errors occurred.
A configuration issue is preventing authentication - check the error message from the server for details. You can modify the configuration in the application registration portal. See https://aka.ms/msal-net-invalid-client for details. Original exception: AADSTS7000218: The request body must contain the following parameter: 'client_assertion' or 'client_secret'.
Cause
The issue was caused by the "allowPublicClient" setting in the app registration being set to "false".
Resolution
To resolve the issue, follow these steps:

- Open the app registration in the Azure portal
- Select Authentication
- Set Allow public client flows to Yes
- Select Save
Note: This setting can also be changed in the app registration’s manifest file
Reference Ticket
35040
Reference Links
Set up Notifications on Critical Errors from the ODX Instance Notifications on Critical Errors – TimeXtender Support