First: do you have a password at all?
If you signed up with Continue with Google, there's no password on your account — and resetting one won't help. Use Continue with Google on the sign-in window instead.
Not sure how you signed up? Try Google first; it takes a second and rules the question out.
Check what you're typing
Make sure the email is the one you registered with.
Passwords are case-sensitive — check Caps Lock.
Passwords use Latin letters only. If yours was typed with a different keyboard layout, the characters won't match even though they look right.
If it worked yesterday and doesn't today
After several failed attempts in a row, sign-in is temporarily blocked — the correct password will be refused too. Wait a while and try again rather than repeating the attempt, which extends the block.
This is also why a suspicious activity email sometimes arrives right after you've been struggling to sign in: those attempts were yours. See If You Get a Suspicious Activity Email.
Reset your password
Use Forgot password on the sign-in window. Requests are limited and there's a short wait between them, so give it a few minutes before asking for another. See How to Reset Your Password.
No reset email? See Troubleshooting Verification Email Issues — the same checks apply.
Still stuck
Write to us at [email protected]. Tell us the email address on the account, what happens when you try, and the exact wording of the error — a screenshot is ideal.
Need help? Contact support at [email protected]