Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
This issue is widespread at the moment.. It seems some hotmail servers are having DNS/ domain resolution issues..
Lets try a fix on just the ipad first.
Follow this guide to change the DNS server. When you get to the point where it wants you to enter the dns servers. Use 126.96.36.199 and 188.8.131.52
If this is the first device you have paired with the Garmin Connect Mobile app, follow the on-screen instructions.
If you have already paired another device with the Garmin Connect Mobile app, from the settings menu, select Devices > in the Garmin Connect Mobile app, and follow the on-screen instructions.
Once you have changed the dns server, try adding your hotmail account agin.. Will it work now?