Help needed with mobile registeration

[Madison]

I have created an account and am trying to register a mobile using
virtual phone within the mobile panel provided. It fails after I reply
'yes' to accept sms from my app (the sms id is tstsms). The error
message I get back is

"tstsms:is having technical difficulties, we received error code 405.
Please try again later"

Please let me know if anyone has an idea as to what might be wrong.

P.S: My callback URL works fine (tested it using a test html file that
submits a post to my callback)

Thanks.

[Simon Wex]

When we send you the HTTP request, it is a POST. Make sure you can
POST to your endpoint. (create a little html form and ensure the
method is POST)

-Simon