The installer from the Captain Sim store asks whether you to select either P3Dv4 or P3Dv5 to installing it to (see attached image). I would have thought that the installer from simmarket would ask the same thing.

If you created a profile using the order number from Simmarket, and the email address used to purchase it there, I'm sure you could have downloaded the latest version of the product using the Extended Download Service without having to purchase it again directly from Captain Sim.

Create Your Profile here: https://www.captainsim.com/cgi-bin/index.pl. When you create it, use your Simmarket order number. If that works, and you can use the Extended Download Service for that order, I recommend that you request a refund for the one you purchased from the Captain Sim Online Store.