A few answers — please keep the questions coming!
We give you a ‘shadow limit’ in the background which is the maximum amount you can pick. This is based on factors like your credit score and our internal data about you. You can’t select an overdraft larger than this amount — but we’ll continually review it too.
This isn’t quite true. If you’re not eligible, we now tell you why you’re not eligible (things like credit score, bankruptcy, CCJs etc). There are some “ineligibility reasons” for which we don’t specifically tell you yet — in these cases you’ll get a generic ineligible message. We’ll add more over time — it’s a case of going down the most frequent reasons first.
We’re very keen to be extremely transparent around this, as far as we possibly can. I hope my answers clear up any misunderstandings!
Yep, totally agreed this is a little strange! As with everything at Monzo, it’s an ongoing project and so over time we’ll get much smarter about knowing your salary — for now, we ask some people to manually input it to help us substantiate our data.
Hope that helps 
Shout with more questions! I’m really excited to get this in the hands of more people and demystify the world of overdrafts somewhat.