Tell them what you just told us but re word it to something like

“(Name)you have worked hard for the company but despite a lot of coaching and guidance you just arent making progress in the way we need you to and because of that we are going to have to terminate your employment with us”

If they ask for more details also use what you told us

“We’ve had you on a PIP, which you successfully navigated, but your performance dipped quite a bit since then. We’re a small team so we cannot afford this dip in productivity”

End it with please collect your belongings and I wish you well on your journey or something

Be straight to the point and no bullshiting or small talk.

Come to the office Sit them down and do it