To communicate to BMC Remedy you must register a OAuth 2 application.
Follow the steps describe here to register the Oauth 2 in BMC Remedy
https://docs.bmc.com/docs/rsso91/configuring-oauth-2-0-799091321.html#ConfiguringOAuth2.0-outh2
For Redirect URI use the URL specified in the Inbound page when creating a OAuth2 Credential.