Even if you did sign something (and certainly do not do it)...it is probably the District Attorney/Child Supprt Division that has the lien againest him....and there is absolutely nothing you can do to release it.
If they don't get paid on your behalf..the lien does not get removed.
And exactly because of a situation like this whereas you might be strong armed into some type of side agreement.

He has already cheated you and your child out of child support - he most likely will not honor a promissory note. He can claim more dependents and get less of a refund. There are organizations that collect child support for people - you probably need to contact them and/or an attorney. I would hate to see you lose out on the money he owes you!

You need legal advice. DO NOT SIGN ANYTHING! No way is this guy going to pay you his tax refunds (if there are any) for the next 3 years. Whatever county you live in, call the child support services and report all this. My heart says you are being scammed. County child support services should not charge you to go after this deadbeat. good luck and god bless!

Forget the loan officer...he works on commission and wants the sale for his sake.

If your son's father, using that term loosely, didn't give you & your son support totaling 25k, what makes you think he'll honor a promissary note after he gets the house? BTW, it's the son's money he's withholding.

Why help the dead beat who won't help his son? Tell him to pay up within 3 years and then buy a house after he gets his "house" in order.

Any way, get an attorney to review anything before you sign! I wish you the best of luck! I have no sympathy for him. Get professional legal advice.