Hi,
It's highly likely that you have problems with setting up you OAuth2 stuff.
Please double-check the
guide and follow carefully again.
Ensure that it is of type "Installed application" as mentioned in this section.
Typically, you shouldn't need to fiddle with redirect URIs, it should just be the default when you create a project on the developer's console.
You may need to check your developer console settings again.
Unfortunately as this is related to security issues, we cannot diagnose OAuth2 problems from our side.
Hope this help.
Best,
Thanet, AdWords API Support