Help about how child support works

I am recently divorced and receive child support. Almost as soon as the check clears my ex is asking for half of the trip he planned for my son, half of his camp he signed him up for, half for the books he needs for summer reading. Basically controlling the child support. I provide my son with health insurance and pay his phone bill every month. One day my son asked his dad to take him for a haircut and he told our son to ask me instead. Is this how child support works?? He sends me a venmo for everything after he pays me? I don't want to involve my lawyer because that costs me hundreds of dollars an hour. We coparent well but he always controlled me financially in our marriage and I feel like he still is. Please give me all your thoughts!