I've answered you on Twitter! For those who's asking: I don't use Unity myself but I know it's possible to adapt a tileset manually if needed. I don't have any tutorials to recommand but you can check with dev communities (for example, the Unity discord :) )
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As I told you on Twitter, if you unlock your dm on twitter we can discuss about that, I can even refund you if you want. I know that a lot of people are happy with this asset pack and I know it's possible to do custom tiles on Unity. So if you're not happy with it I get it, but please don't tell that it's unusable :/