Redirect request to another endpoint

I have 2 endpoints that read XML from the request body.

APInvoices

ARInvoices

I need to create another endpoint, call it PostInvoices, that reads the same XML and queries some values and redirects the query to either ARInvoices or APInvoices. Each of the two endpoints respond with XML output which I'd need to pick up and respond back to PostInvoices.

Is that something that is simple to do? Haven't found anything useful on the web about it but then it's hard asking the right questions sometimes, if you don't know the right terms.