I've noticed that the content that is in all of the D&D books is needed to be bought here. I just wanted to see if there would be a way to implement a proof of purchase feature or whatever because I didn't want to pay for the book twice when I already have it at home. This is such a simple idea I'm sure it was already proposed and it just didn't work out because people could cheat the system but I thought I would post it here.

D&D Beyond is not WotC. Proof of buying from somebody else doesn't mean anything. They have to pay a license to give you digital access, so they're not going to give it away for free (since they have to pay to do so).

They were part of a big one-off collaboration for an Essentials Kit that could be bought physically and had a code to unlock the digital version of the adventure plus a code for 50% off the digital PHB. However, it's special one-off and not something they can do for all books.

If you have the physical books then you can use the digital homebrewing tools on here to recreate those options for free personal use. Or you can buy just those individual options in the marketplace.

There's like a bajillion threads on this already so if you want more info and discussion consider a forum search.

Thanks for this genuinely, I didn't think about homebrewing the exclusive things. I knew there were bound to be other threads and reasons this wouldn't work and so thank you for informing me of why.