I always liked the simple 3e tiers approach. Hostile / Unfriendly / Neutral / Friendly / Helpful.
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It won’t model negotiating a treaty. But as a way of getting a person you’ve never met or who is unfriendly to undergo some task for you then it’s a good shout.
Social skill check with DC depending on the severity of the favour/task being asked. Allow the individual to suggest alternative stats if appropriate.
Usually automatic successes if Helpful, Usually automatic failure if Unfriendly
Advantage if Helpful, Disadvantage if unfriendly.
Then a reworked skill check DC to improve tier.
Hostile 20 to improve to unfriendly, 25 to unfriendly
Unfriendly 15 to improve to neutral, 20 to friendly, 25 to helpful
Neutral 15 to improve to friendly, 20 to improve to helpful
Friendly 15 to improve to helpful.
Failure by 5 reduce by 1 step instead
Roll a 1 and become hostile.
This is all just off the top of my head, cribbed from 5e.