I am trying to use External Services with Flow. The schema file includes a body. I do not know how to set the body using variables I have created. The body only allows a single apex defined variable input. There is no body apex defined variable generated by the schema. I am not sure if one is needed.

I am new at this. Any idea how to use flow to set variables to an esternal services body during a Post call out?

I am happy to share my schema file. Any help will be greatly and gratefully appreciated.