The above header refers.
I have checked all the issues listed below and they are as was advised, yet the app still cannot connect to my site.
Assuming you have enabled mobile services on your site, please check:
1. If your site uses an SSL certificate, it must be a trusted certificate, not self-signed. Please use these tools or a similar one to check that your certificate is fine: SSL Checker and SSL Server Test. All the checks must be ok, including the "Certificate Chain Complete". Otherwise the app might work on iOS but not on Android.
2. Debugging is disabled (in Site administration > Development > Debugging)
3. The ADOdb debug option is disabled if you are using the external database auth or enrolment plugin (in Plugins > Authentication > External database and in Plugins > Enrolment > External database).
4. SHA-1 https certificates are not supported anymore in Chrome, this means that the Android version of the app won't work for your site. If your site doesn't work in desktop Chrome or Chromium it won't work in the Android app. See https://blog.chromium.org/2014/09/gradually-sunsetting-sha-1.html for more information
5. If you are using IIS check that Anonymous access is not disabled for the /webservice directory.
If you still have a problem, please post in the Moodle for mobile forum.
So, what do I do next?