REST API Request Using Invoke-RestMethod

I'm having a devil of time formatting a request to a REST API. I've tried twenty different ways of passing the request information in headers\body using Invoke-RestMethod. Here's what the request needs to look like:

PUT /api/v1/files/cliScript/incremental
Content-Type: application/octet-stream
<show system uptime>

I can't figure out how to pass these SHOW SYSTEM commands. Has anyone tackled something like this before?