What is the true issue with child support?

This is the breakdown,
The man and woman both don’t do not want to be together. They decide to go through with the pregnancy.
The child lives primarily with the mother. The custodial parent.
The father has access to the child. But has not been around. The father has all the phone numbers school information but has not been around.

Now the child is getting older These are get expenses for the mother and want to place the father on child support.

Where is the issue?
Updates
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History some backstory to this scenario. The mother was working living on her on and the father was also. They meet dated but determined it wasn’t not a match but unplanned pregnancy. Fast forward wanted to be co parent, but by nature she have the baby she breast-fed the child was sent home with her. There were no courts until the point of her having hard time due to savings and maternity leave being over.
What is the true issue with child support?
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