A link from our FAQ was provided when you created the bounty:
If you do not award your bounty within 7 days (plus the grace period),
the highest voted answer created after the bounty started with at
least 2 upvotes will be awarded half the bounty amount. If there's no
answer meeting that criteria, the bounty is not awarded to anyone.
the bounty was started by the question owner, and the question owner
accepts an answer during the bounty period, and the bounty expires
without an explicit award – we assume the bounty owner liked the
answer they accepted and award it the full bounty amount at the time
of bounty expiration.
In any case, you will always give up the amount of reputation
specified in the bounty, so if you start a bounty, be sure to follow
up and award your bounty to the best answer!