When GRANT TYPE is selected as Client Credentials, currently we don't have an option to select Client Authentication method.

Migration : To select Client Authentication option by default as Send Client Credentials in body for GRANT TYPE : Client Credentials.

Edge case : Currently the Client Authentication option is working as Send Client Credentials in body for GRANT TYPE : Authorisation Code, even if we select Client Authentication as Send As Basic Auth Header. As mentioned below if a customer uses Facebook or Slack IDP and in their Client Authentication option if they have selected Send As Basic Auth Header it would have worked, after this update it won't work they would need to change the option back to Send Client Credentials in body because Facebook and Slack support only the option Send Client Credentials in body
IDP Providers

Support Both Client Authentication option ( Send Client Credentials in body & Send As Basic Auth Header. )
( Google, Microsoft (Azure AD), LinkedIn, Dropbox, Okta, Auth0, Amazon (Login with Amazon)

Support only Send Client Credentials in body
( Facebook, Slack )

Support only Send As Basic Auth Header
( Spotify, Reddit, Apple )