When trying to update the manifest file of my Azure AD application, I receive the following error (see screen shot):
Failed to save manifest. Error details: KeyValueMustBeNull"
I am attempting to update the 'Value' attribute of the keyCredentials in the manifest, but it will not allow me to do so. It will let me upload a manifest with the Value set, but then it wipes it out and resets it back to null. I have duplicated this problem on both the new Azure Portal and old management portal.
How can I fix it?
While the instructions you linked above look similar to this, I would try following these instructions as they have worked for me in the past when trying to add Certificated to my application.
Note that this uses the old Azure Management Portal versus the new Azure Portal which it looks like you are using.
Let me know if you are still getting the same error after these steps.