The same in different browsers. If this redirect uri is mandatory than i cannot use your implementation unfortunately.
Yes, redirect uri is a needed field for generating access token. Just to confirm again, you are adding redirect url in the field and save the details using Save button. That does not work for you? See attached screenshot.
Dont think that asking google about this will help.
Asking help is not an issue but not sure how long it will take to get a response. You can check on Google forum about this issue and try the given solutions.