Please make sure you do not start working until the client pays the deposit.
Unfortunately, we are not able to help you with an unpaid invoice The contract starts when the client pays the deposit. Until then, Useme is not legally a side of the deal. If you have signed a contract outside of Useme, you can seek your rights by civil proceedings.
To avoid this situation next time, choose the Sign a contract path in Useme. This way, the freelancer doesn't start working until the client pays the deposit. We keep the work and money safe.