For security reasons or as a precaution, you may wish to generate a new Secret Key for your Primary Account or Sub-Accounts. To reset your Secret Key, simply go to Account settings → API Key Management (Primary and Sub-accounts).
Click on the cogwheel and then select “Reset Secret Key”.
A popup window will appear, asking you to confirm your action by typing the confirmation phrase "RESET". You will also be informed that the new Secret Key will be effective immediately and you need to modify your API and/or SMTP configuration accordingly.
Note: you need to type RESET in all capital letters or you will get an error message.
Once you confirm the reset, the new Secret Key will be displayed only once (until you close the popup window), so be sure to save the new key in a safe place for future use.