I have 4 (self-published) books available on Amazon. If you are happy with ebook versions (including hyperlinks to the answers), they are included for free in 4 of my courses, and you can pay me with Bitcoin (10,000 zaps will give you lifetime membership of any course). If you want a hard copy, I'm afraid you will need to pay Amazon in fiat. Sorry about that! One day, I hope to take Bitcoin for hard copies too.

https://www.amazon.co.uk/gp/product/B0CKNGNGL8/ (MASTER GRAMMAR)

https://www.amazon.co.uk/dp/B0C7S44SQM (MASTER VOCAB) https://www.amazon.co.uk/Grammar-Theory-Practice-David-Nicholls/dp/B08QWK88NQ/ https://www.amazon.co.uk/Visual-Phrasal-Verbs-Black-white/dp/1097343499/