Can a contact re-opt in to receive a campaign after opting out?

I had a contact opt out, and then came back later and through a KEAP wordpress form complete a request and optin to get a free lead magnet. The system did not send it, according to keap support Dexter, because the opted out. That seems contrary to how email optin and opt out should work. His answer was for me to manually opt in that contact, but that would be almost impossible to manage if you are doing a big campaign — to find any and all that requested it and the didn’t get it.
Is there a way through the set up of a web form or landing page, If a contact has opted out and comes back later to purchase another product that has an automated delivery sequence to it?
I thought the only ‘proper way’ to get them to opt in again was for the contact to manually opt themselves in again, and it was frowned upon for the keap account owner to change their preference and opt them in if they had opted out.

If they opt back in from a WEB FORM they can opt back in, but not via anything that is via an API connection.