[Solved] How to hook into Commerce after payment complete

I need to be able to run code that does not output any data to the user after a user’s checkout is complete, but I can’t seem to figure out how Commerce wants me to do it. I don’t see any *.api.php files that would give me payment hooks. It looks like Commerce wants me to create a separate Checkout Flow plugin that would add the step I want, but I can’t seem to find documentation about implementing my own Checkout Flow.

Can you guide me to the right path of running my code when the checkout is complete? Am I on the right path? Can you point to Checkout Flow development docs?

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