If you’ve missed a campaign session or otherwise fallen behind in XP compared to the other characters, you can spend downtime adventuring to help catch up to the other PCs. Usually downtime adventures feature encounters that are much easier than you’d normally expect as part of a group. For example, a 5th-level character might clear zombies out of a crypt or assist some lower-level adventurers with a problem that’s a little too difficult for them.
Spending 1 day of downtime adventuring earns you XP as if you had defeated an opponent whose CR was equal to your character level. For example, if you are a 3rd-level character, you would earn 800 XP. You do not earn any treasure or other capital for downtime adventuring.
If using this downtime activity would increase your XP above the highest XP value among all the PCs in your party, it increases your XP to that value instead; any XP earned beyond this amount is lost. This activity allows you only to catch up, not to get ahead.