When attempting to create a Review App, you see an error saying "Couldn't create this review app: Name is already taken" despite no apparent naming conflicts.
This often results from either closing and quickly reopening a pull request, or selecting Create Review App button while it is already in progress in the background.
You should be able to resolve this by closing the pull request, waiting 30 seconds, then reopening it. This should delete the original app, clean up, then recreate it.
You can also manually delete an app from the settings tab of your app dashboard -