I am using grant type=client_credentials but i get the following error when i debug the code i see there ia s failure on that assertion otk grant type = client credentials
"error": "unsupported_grant_type", "error_description": "The given grant_type is not supported by the server."
Something must be wrong with the request you're sending. Have you tested the Oauth Test clients including client_credentials (https://gateway.domain.com:8443/oauth/v2/client) post installation?
A properly installed oauth toolkit should work with below request.
First test the Test Clients at https://gateway.domain.com:8443/oauth/v2/client and make sure all the grant types work.
If not working, you still have some post installation steps to perform.
If that works, then try to make the call manually using a REST client for client_credentials grant type.
OAuth Request Scenarios - CA API Management OAuth Toolkit - 4.2 - CA Technologies Documentation