It's the 76° mission in chronological order of the RDR2 story mode, played with protagonist Arthur Morgan .
While optional for story progression, this is an Optional Honor Mission required for the "Lending a Hand" Trophy/Achievement. It's a time-sensitive and missable mission, so it can only be played at this specific point in the story.
Money Lending and Other Sins - VI & VII - Mission Details:
Strauss at Camp gives Arthur the details of two new debtors.
J. John Weathers can be found near Moonstone Pond, to the west. He is trying to repair his broken wagon on the side of the road. When you confront Weathers, a group of soldiers searching for him launch a surprise attack. Once the dust settles, you have to choose between absolving or recovering the debt.
To search for Arthur Londonderry, head to the entrance to Annesburg's mine. After questioning the guard, enter the pit and speak to the foreman.
Your next destination is the debtor's widow, Mrs. Londonderry. She lives outside a small cabin at Butcher's Creek - a short ride to the south of your current position.
After a conversation, Arthur automatically decides to absolve her, but you can also choose to give her money too; doing so costs a nominal dollar sum but rewards you with 20 honor points.
Return to Strauss at camp to complete this mission strand.
Gold Medal Objectives (100%)
This mission does not feature Gold Medal objectives and is not replayable.