Variables in OAuth2

Hello All,

I have create an API Call using OAuth2 as authentication method. FOr the client ID and Client Secret i ahve set variables additonally, as the belo screenshot.

The token genrated succesfully, but i got the same notice for these two fields.
“The field contains characters that might need to be percent-encoding depending on the authentication server”

Can you help me which is the reason(s) and how can i solve it?

Thanks in advance!