However in Prometheus Im been thrown errors on "Unsupported Media Type"
msg="non-recoverable error" count=9 exemplarCount=0 err="server returned HTTP status 415 Unsupported Media Type: <!doctype html><html><head><meta http-equiv=\"content-type\" content=\"text/html; charset=UTF-8\"><title>415 Unsupported Media Type</title></head><body><h1>Unsupported Media Type</h1><p>The requested URL does not support the media type sent.</p></body></html>"
Your Prometheus config is sending the data to port 8089 -- the main Splunkd port, rather than the prometheusrw port.
The prometheusrw input opens up a new port (8098) that can handle the content-type that Prometheus will send. You need to update your Prometheus configuration to use port 8098 and (in this case) use http and not https.