I've talked about boundaries before... but what does that look like for a coparenting relationship?
I'm a big advocate for coparenting, but I also have the mindset of protecting my children and their peace. One thing I've learned is, you can't make someone be a parent if they don't want to. You can't foster a relationship between a child and parent, because it isn't your responsibility. My job is to solely be their mom, I can't be their dad too. All I can do is protect them from low quality experiences that could affect them longterm.
As the full time parent, it's important to establish boundaries and expectations. Letting your fellow coparent know what you will and will not accept should eliminate confusion as to what is expected of them. I say should, because sometimes you can do everything fair and it still not be the outcome you're looking for. If the other parent isn't willing to do what's necessary in the child's life and you have to repeatedly make up where they fall short, it is important to create boundaries that don't put you in the same position.
Remember, you aren't closing a door that was never fully open.