Due to previous issues impacting Trainers encountering certain Pokémon during Raids in Pokémon GO, Niantic has announced that you can receive up to two free Raid passes per day from September 7 at 1 p.m. PDT to September 8 at 1 p.m. PDT. Read on below for the official announcement from the development team:
Due to previous issues impacting Trainers encountering certain Pokémon during Raids, from 9/7 1 pm PDT to 9/8 1 pm PDT, you can receive up to 2 free Raid passes per day. Thank you and we apologize for the inconvenience.
Source: Niantic Support @NianticHelp
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