Some Raid Bosses are difficult to defeat, so you may not be able to beat them on your own.
Raids have 4 tiers of difficulty: tier 1, tier 3, tier 5, and Mega Raids. The higher the difficulty, the stronger the Raid Boss and the more players you’ll need in order to succeed. You can tell how difficult a Raid Boss will be to defeat by symbols that appear under their portrait on the Nearby screen.
If you aren’t able to defeat a Raid Boss on your first attempt, you can rejoin the raid and battle again. You won’t need to use another Raid Pass to rejoin; your pass will grant you access to the battle until the raid’s timer runs out. You can join as many times as you’d like before the raid’s timer runs out.