I've changed the category as payment pursuant to a divorce decree is generally not a debt settlement issue and payment instruction should be in the decree.
The payment should be traceable, so make sure you are using a check to pay. I would also take advantage of the memo line and write something along the lines of "full settlement of divorce pay out". If your ex had an attorney, I would recommend going through them by writing a nice cover letter stating that the check is the payment and that you would ask them to forward the same to your ex. That way they have a record of the fact you sent the check and if your ex comes back claiming you did not pay, his/her attorneys know that is not the case. You should also keep a copy of the check and the cover letter for your own records. Sending it by certified mail and keeping a copy of the green card that gets returned to you so you have proof it was received is also a good idea.
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