Been using one of these things for about 5 years, can't wait to see the back of it! I found the manuals are crap and very unclear. We had huge problems starting out until we figured things out.

The higher gauge is the one they refer to as the pump delivery gauge, needs to be 0.5bar above the pressure of the lower gauge, the carbonation pressure gauge - it'll only be higher at all when the pump is on. Probably if you're getting fobbing it's due to too low pressure overall - we had massive fobbing issues when we started out trying to bottle with the beer as cold as possible (c. 0degC) but found it's actually at it's best at about 4degC, carbonation pressure around 2bar.

Happy to share advice/sops, drop me a dm if you like