Hi,
Can you please confirm if you are working on a Win OS or Mac OS?
In the meanwhile, try to launch Captivate 2019 again and once you have reached the 'Sign in required" screen, then select the option "Not your AdobeID" and Sign in again with your Adobe Id and Password and see if that works.
Let me know if it still prompts for the serial key.
Regards, Ajit
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