Welcome to TuD, @Maddy1! It looks like you are stuck setting up NightScout with your DIY Omni-Loop. What instructions are you following?
These are the instructions that I follow. I don’t use Omni-Loop but instead use an old Medtronic pump with the DIY Loop. Most of the instructions for both the Omnipod and Medtronic are the same. I’ve successfully used these instructions. I’ve not been through this process very often, so I can’t recall the steps from memory.
There are two FaceBook groups that may be able to help you: CGMinTheCloud and Looped. Someone here may be able to help but I think your chances would be better on those two venues.
Didn’t Nightscout kill off the mongolabs thing? I remember having to migrate to Atlas instead. I use Nightscout, but not for looping, so I might be missing something.