The POST /{envID}/saml20/sp/acs operation is a service provider (SP-initiated) SAML single sign-on flow that passes the application ID and (optionally) the application URL in the RelayState post parameter in the body of the request.

The RelayState parameter needs to be in the URL-encoded format of applicationId=<your-appID>. For example: RelayState=applicationId%3D280686bb-cfca-4825-88a1-67dc1c89c73c, where “%3D” is the URL-encoded value for “=”, and “%26” is the URL-encoded value for “&”.