Way to connect mailerlite automation with digital product purchase?

Hey, without using Squarespace campaigns, is there a way to trigger an automation with mailerlite, similar how you may with a freebie?

I am looking at moving my freebies into a shop with another paid product and wanted to keep it all seamless on one page, but can't seem to find a way to retain the sequence. I was looking at zapier but a bit unclear as to the cost (if any) and if that zap would work. ie. client 'pays' for free product and then its sent via the digital products download. But then I want that person to be added to my welcome sequence with mailerlite that I already have set up.

Thoughts? Thanks!