How to return authorised scopes from a list of requested scopes

I have an api where different methods are protected by different scopes. For example some methods are only allowed when an ‘admin’ scope exists.
I have an angular(7) spa with Implicit flow. When users login both the ‘standard user’ scope and admin scope are requested. However if I login as a standard user I recieve an unauthorised scope error. How can I configure the authorization server to return the allowed scopes and not an error?