Kieran,
All the problems I've had communicating with backpack have had to do with using the right security protocol. For a while, we solved it by disabling secure communications. Then we were able to use the proper protocol. (I'm not a system guy, so I don't completely understand all the details.)
Here is the thread of that issue:
https://moodle.org/mod/forum/discuss.php?d=253564
Bill