I would ask them give you 25-50% up front then the remaining after they have accepted the finished work. I don't know the nature of your work but maybe you can

I would ask them give you 25-50% up front then the remaining after they have accepted the finished work. I don't know the nature of your work but maybe you can give give them 50% half way through the schedule and they give you the pay for that work, then you give them the remainder when it's done and they pay you back. I definitely wouldn't trust them with all my work/result and then hope they'll get around to pay me.