What are the most common ways seller notes are made forgivable?

Examples I've come across:

If revenue is less than $3mm, seller note balance and all interest are void and forgiven reducing the note value to $0 and eliminating the debt obligation fully.

If DSCR falls below 1.5 in Y1, reduce seller note by $500k. If DSCR falls below 1.5 in Y2, reduce seller note by $500k.

I know one size doesn't fit all, so I'm asking for collective wisdom on what has worked in your deals.

All thoughts appreciated.