This has been resolved. Everything came down to a server side issue. Axios was in fact sending the POST, however Apache ModSecurity was rejecting the request resulting in a redirect which changed to a GET request, which explains the GET result I was getting in the console error logs.

This post explains in more detail but the issue was linebreaks not passing through the json and flagging ModSec. Once I added an extra scape ("\") to \r\n everything worked smoothly.
ModSecurity fails to parse request