Getting InvalidKeyCertPair error with bugged message: "{0}" when trying to upload a cert pair.

[#1]

When giving (what I'm fairly certain appears to be) a valid .pem and .key archive to this route, via a curl, I get the following response:

{
  "code" : "messaging.config.beans.InvalidKeyCertPair",
  "message" : "Invalid Key and Cert pair. Reason : {0}",
  "contexts" : [ ]
* Closing connection 0
}

The only semi-helpful information is the code, but even googling that yields no helpful results. The message field seems to be bugged, unless I'm mistaken.

Can anyone offer more insight to this problem?