So Max Conversions is pretty temperamental (similar to Target CPA, but in different ways). I’ve found that Max Conversions does really well when you have 30-50 conversions in the last 30 days. That’s the first step.
If you have that, then the next thing to know is that you need to always start with a LOW budget for Max Conversions. Because the goal of Max Conversions is to get as many conversions *for the budget* of the campaign, it will always try to spend that entire budget, regardless of whether it thinks it can get 5 conversions or 50 conversions that day.
I begin with a low budget and within 7 days or so it starts performing really well. Then I slowly (repeat, SLOWLY) start to increase the budget, with the understanding that it will cause performance to go crazy for a few days before it catches again.
Honestly, Max Conversions is the biggest surprise to me in the last 2-3 years. I was sold on Target CPA as the holy grail… until I tried Max Conversions, because then my entire account CPA decreased by 10-20% and my margins improved as well.