I've added Audience parameter from advanced options but I don't see a parameter added in the postman console.
Below is a sample request & highlighted in bold is the parameter that needs to be added on the authorize request in postman.
https://{ehr_authorize_url}?
response_type=code&
client_id=app-client-id&
redirect_uri=https://{app_redirect_url} &
launch=123&
scope=openid+fhiruser&
state=abc&
aud=https://{fhir_base_url}&
code_challenge={XXXXXXXXX}&
code_challenge_method=S256