The opening mission for Hosea has Matthews and Arthur Morgan tracking down a huge bear, but it's the second mission that has you unlocking a Fence, after you've completed the mission by successfully stealing a wagon. After Hosea's second mission has been completed, the Fence will always be open for Arthur to use.

What mission opens the fence in rdr2?

In Chapter 2, complete Hosea's second mission, The Spines of America, to unlock the first Fence.

Which rdr2 fence pays most?

The Saint Denis Fence can be found in the market in the east of the city. This is certainly the most successful Fence in the game, considering that he isn't working out of some kind of makeshift, untoward building.