If this is a simple http interface (no soap, no SSL), you can use the http-client protocol along with the httpQuery TPS proc supplied with cloverleaf.
Turn on “await replies” and set a time out, the proc has built in logic to use those keys out of the NetConfig.
The reply from the post will get passed back to the engine via the Inbound-Reply stack. You can use the recover33 procs, you may have to modify the IB-reply proc depending on how the reply is formatted.