In order to connect to Redmine server via HTTPS/SSL with self-signed certificate you need to add that certificate to your Windows Phone device first.
Follow the steps below:
On your desktop, run Internet Explorer "as administrator" (Important!):
Navigate to your Redmine, if you will be prompted with security warning click "Continue to this website":
On navigation bar click website certificate icon, then click "View certificate":
Click on "Details" and then on click on "Copy to File..." (if "Copy to File..." button is disabled this means you forgot to run IE "as administrator"):
Certificate export wizard will appear, click "Next":
Make sure you have "DER encoded binary X.509 (.CER)" selected and click "Next":
Select where certificate will be saved (e.g. your Desktop).
The name of the file should match your Redmine domain name plus CER extesion (e.g. redmine.yourcompany.com.cer). Click "Next", then click "Finish":
At this point you should have your certificate file (.CER):
Now you need to transfer this file to your phone. The easiest way is to send that file via email to your live/gmail email account registered on the phone.
E.g. right click on that file on your desktop and select "Send to" -> "Mail recipient" and type your email.
Check you mail on the phone and locate that attachment you sent in previous step:
Tap on that certificate attachment to download it and then tap it again to install it.
Open IE on your phone and navigate to your Redmine, make sure you have no warnings.
Now you should be able to connect to your Redmine server with Redmine To Go.