LTI and Moodle

I have a Moodle provider course set up, and am trying to consume it my MoodleCloud instance, but it only displays a "Refused to connect error"

• Provider Cartridge URL: 
  • https://sampledomain.com/enrol/lti/cartridge.php/1/1f8828ae716171f0a7bb5afc15e05974/cartridge.xml
• Secret:
  • 0451fliTuagzDeXfDMHA3UUGdiWBqUeX

• Registration URL
  • https://sampledomain.com/enrol/lti/proxy.php/1/4dce7c3b4af221ce330ccad999e0fbf4/

I've put in the Tool URL (trying both Cartridge and Registration, in case there was a difference) and it still returned an error "sampledomain.com Refused to Connect"

In the settings in the consumer - the tool URL has been changed to "https://sampledomain.com/enrol/lti/tool.php?id=1" and displays "Tool Configuration not found for this URL". I assume this might be causing the issue, but I don't know how to stop the URL from being changed. 

I have succesfully set up LTI in the other direction - Moodlecloud instance provider, Moodle consuming.

Any help appreciated.