This question gets answered online with invented numbers. We will not join in.
What is fixed. Your share: 30–60% of net ad revenue, depending on your ad share. The more airtime you release for advertising, the higher the share.
What depends on your location. The daily price of your screen and how often it gets booked. A screen with a queue in front of it sells better than one in a corridor.
The maths. Daily price × your share × days booked. Two of those three you do not know at the start. Anyone quoting you a monthly figure anyway is guessing.
What we are allowed to say. Our screens have already been fully booked out. That is history, not a promise for your screen.
What you lose in the bad case. Nothing. No monthly fee, no setup cost, no minimum volume. The stake is your airtime, not your money.