How to be taken seriously when handling a debt owed by an ex friend?

I helped a friend during hard time and they help continued for a year and half. He needed help with bills, rent, etc. As he has 4 kids, is on ODSP, and can only work part time. We decided that I would hire him to work for me in early 26. In the meantime he started a second job. Our agreement was that he pays me back when I hire him. He also said in both writing and verbal that he would give me half of his tax return when he gets it, in 2026. Since the money he owes me is exceeding 12,000. He was recently introduced to a new person in his life who is abusive and extremely controlling. Which led to him kicking me out of his life. Talking to him has been difficult but we remain friendly when it comes to discussing the debt. He told me that he doesn't want to work for me anymore. As the new person is jealous and thinks I want to be more than friends.

Friend at first said he would follow through with his words but then said he could only refund me 50$ a month. Which would lead to the repayment of the debt in 12 years or something.

I've been understanding of his issues with money, and proposed that he pays half of his tax return like we said, and then we could work on a small amount per month, in good faith. He said good faith would be to actually pay me back. I know and understand this is a small court claim thing. I really hope it doesn't get to that. I still care about him and hope our friendship will return again.

I'd like to know what are the gentle, but firm ways to inform him that I will only accept one payment plan. Like a formal letter. Since our discussion can be slow and stagnant.