To add an API key to your user account, click on your profile icon > My Profile.
Once in the user profile screen, click on the API key icon to generate an API key.
Check you are not a robot and hit Update to commit the changes.
If you plan to use the API key for the Megaventory mobile app, you should also add a Mobile Pin (4 to 6 characters long, all numbers). If you are not the admin of the account, tell them to set a Mobile Pin for you since the mobile pin can only be added for a user by the admin of the Megaventory account.
Always click on Update to commit the changes.