I am following https://developer.github.com/apps/building-github-apps/creating-github-apps-from-a-manifest/#implementing-the-github-app-manifest-flow which works on github.com to initiate creation of an app for an org. When I try the same flow on GHE, just with the URL substituted to include the GHE domain, I POST a JSON manifest to https://github.mycorp.com/organizations/TESTORG/settings/apps/new and the server responds
Your browser did something unexpected. Please contact us if the problem persists.
Note that a GET request to the same URL gives the expected form Register new GitHub App.
Is there some way to diagnose the issue? Is the problem really about “my browser”, or was there some incorrect data being uploaded? Does GHE (in this case 2.20.6) even support the app manifest flow? (This suggests that it does.)