Going through a divorce and he served me paperwork saying he will pay $300 per month for 3 children. I should wait to go to probation before signing

If you and he agreed that he would pay for specific expenses for the children, then everything agreed upon needs to be in a writing submitted to the court so that it is clear what he is to pay for. If its not in a writing as part of the submission to the court, he can later claim that he never agreed to pay for those expenses and a judge will be hardpressed to impose an obligation that you say he agreed to and he says he never agreed to do so.  Separately, you and he NEED to run the child support guidelines as part of the divorce process so that the court and both of you know exactly what he was obligated to pay under the guidelines. You and he have the right to deviate from those guidelines, but for court purposes, it is required to be submitted and referenced to the court. The guidelines identify your income from all sources, his income from all sources, who is paying for the childrens share of  health insurance coverage ( and the actual amount for their share of the coverage) and the number of overnights the kids will be with him over the course of the year( i.e - if he has them every other weekend from friday to sunday, then he has 2 overnights in a 14 day cycle or 52 overnights for the year).