I payed for 4coder a long time ago, but did not manage to make the switch. I would like to try again. I have access to the full version 4.0. However, version 4.1 seems to be a different product on Itch. Is it meant to be that way, i.e. do I have to pay again?

Yes, you need to pay for 4.1. But it will become free in a few month.

Okay, thanks.