This should have been in your agreement. The judge can't enforce something that isn't in your agreement.
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Then your mediation agreement would appear to be incomplete. See a family law attorney, if you do not have one, about possibly having the Final Judgment amended to address this issue immediately.
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Figuring out the problem is at least half the trick of answering these questions. I take it he has agreed to pay you $6000 but the mechanism by which the payment is to be made was not spelled out. This means to me the agreement was not complete, and unless he is willing to a further agreement, the judge will not graft something onto the final order. My advice would be to get a lawyer to help with this problem.
The amount owed to you needs to be established as an arrearage (money owed to you) in the Final Judgment. Ask the Judge to do this but be prepared to show that he owes you this amount. During the same hearing, you may ask the Court to award you the amount payable by way of an Income Withholding Order as long as same is for back child support or alimony not any amount he owes you towards a debt such as a credit card or mortgage.
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