Hello @NoahC, welcome to the Let's Encrypt community. 
Do you have some geo blocking?
Please read these:
Edit:
And using the online tool Let's Debug yields these results
https://letsdebug.net/radio.youaremachines.com/1964683
UnexpectedHttpResponse
WARNING
Sending an ACME HTTP validation request to radio.youaremachines.com results in unexpected HTTP response 403 Forbidden. This indicates that the webserver is misconfigured or misbehaving.
403 Forbidden
<html>
<head><title>403 Forbidden</title></head>
<body>
<center><h1>403 Forbidden</h1></center>
<hr><center>nginx</center>
</body>
</html>
Trace:
@0ms: Making a request to http://radio.youaremachines.com/.well-known/acme-challenge/letsdebug-test (using initial IP 45.55.196.154)
@0ms: Dialing 45.55.196.154
@195ms: Server response: HTTP 403 Forbidden