California law requires that employees be paid the minimum wage each hour they work. Your system would be acceptable as long as the employee is guaranteed $8 per hour for each hour they work if they do not get enough leads to equal that number.
Good luck to you.
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Best thing to do is pay $8.00 per hour
This is not intended to be legal advise or as legal representation. I am a California personal injury attorney . Be aware that every state has its own statute of limitations; and statutes & case laws that govern the handling of these matters.