The code has not arrived
Check spam first. Then use Resend — there is a short cooldown between sends, which is why the button is briefly disabled.
If it still does not arrive, the address may not be the one on the account. A code is sent to the address the account holds; a typo at signup sends it somewhere real and silent.
The code is refused
Use the most recent code. Requesting a new one invalidates the previous, and typing the older one from further up your inbox is the usual cause of "invalid".
Codes also expire after a short window. If yours has been sitting for a while, request a fresh one.
Too many attempts
There is a limit on how many codes you can request in an hour and on how many times you can get one wrong. Passing either locks you out for a period, and each subsequent lockout is longer than the last.
Nothing clears it early — not a different browser, not a different network. Waiting is the only remedy, and this is deliberate.
Wrong role
If your account holds more than one role, pick the one you actually use. Forgot password is scoped the same way: choosing a role your account does not hold tells you so rather than sending a mail that never arrives.
Signed up with Google
Use the Google button every time. An account created that way has no password until you set one, so the password form will never work for it.
Still stuck
Open a ticket from the sign-in page, or use the contact form. Include the email address you are trying and roughly when you last tried — that window is what makes it findable.