Depends what is understood by ' co-parent ' ?
I understand it to mean parents are divorces, but the absent parent wants to be involved in raising their child.
My advice would be to link involvement to compliance with child support payments, but also to put in writing the principles and practices of child raising.
That is the bedtimes for appropriate ages is spelt out, diet and snacks, what is appropriate behaviour and how non compliance by the child or the other parent is to be dealt with.
I suspect the various conditions will have to be negotiated, but once agreed each co-parent should have a signed copy of the parenting document and if needed to be registered with the divorce court.
I Don know of any parents being Co- parents, so the above is just a suggestion,based on knowing that clear communication is vital in marri and in child rearing.