I recently got a job where I get paid either a base pay or a commission (incentive) pay (I don’t get both per paycheck, either one or the other).
Most of what I make from the job is from the base pay, which is $20 per appointment. But the issue is, I don’t get paid the base pay if the client is below the age of 30.
So if we go through an appointment and they’re below 30, and they don’t buy anything, I get paid nothing.

If my client isn’t 30 or older, is it haram if I lie on my appointment bookings and say they’re 30+ so I can actually be paid? My family is going through really tough times right now, and I need to make money for them.

It is not permissible to lie or use any other such means in order to earn a living or carry out any transaction for that matter. Islam strongly obligates that we follow the terms of a contract irrespective of how hard it is on our lives. I pray that Allah makes it easy for you, remember that if you remain within His boundaries, He will reward you and open a door, insha-Allah