With nonpayment of child support, the only proof necessary to establish nonpayment is sworn testimony. When a party alleges that the other has not paid their support obligations the Court looks to the payor to prove what was paid, not the payee to prove what was not. In simple terms, if you owed $500 per month in child support and I sued you for contempt and said you had not paid, that’s all I have to do, and the burden shifts to you to prove you did pay what was Ordered and owed. If you cannot prove it, you may be out of luck.
The defense is normally, “But I paid cash…”. The other party is not going to admit that you paid cash or if you did it was because you owed them money, not that it was the child support payment. The best piece of advice is to get a receipt everytime. Hand write it on notebook paper if you have to. Keep good records of how much was paid and on what date it was paid. Your wallet and your freedom, at least temporarily, may depend on it.