Check your inventory; if you have already claimed it, the system will output: “Post Office Password already used.” Tips to Maximize Password Rewards
If you want to find passwords "legitimately" or stay up to date without spoilers:
Scroll past the standard player-to-player mail UI to reach the text field. Carefully paste your chosen phrase from the lists above. Tap Submit Password .
Note: Some passwords are "case-sensitive" or require specific farming levels to redeem rewards.