If you've entered your API key and it continues to come back invalid, make sure that you have verified that it is your correct key in it's entirety.
If that still doesn't work, make sure that your Torn ID (The number found at the top of the settings page) matches your Torn ID in game. If these numbers do not match, you won't be able to validate your API key. You must either delete your account and register again with the correct ID or contact a staff member on Torn Stats' Discord to help recover the account already using your ID.

You can find your display name in your account settings page.

Your API key is located in your settings page on Torn. Make sure you copy the entire key and paste it here on Torn Stats.

You can find your faction listed under Factions -> View Factions, or you can find it directly by asking your leader for an invite link to the faction.

You can report a bug by contacting a staff member on Torn Stats' Discord.

You must provide an API Key that is at least a "Limited Access" level API key. Public or Minimal access won't work as they don't provide access to the stats necessary to make Torn Stats useful.