Using crypto for payments on my site

I'm curious if anyone here has ideas on how to add cryptocurrency as a payment option on my website. Like, if I were running Amazon and wanted to accept Ethereum, Bitcoin, and USDT as payment. What’s the best way to go about it? I bet there are existing services that can help with this. I just need to figure out how I can set up my own payment solution.

You can Use existing crypto payment processors.  Thats thes most recommended method for most businesses. the payment processor will help handle the complex technical aspects wallet management, blockchain monitoring, fiat conversion, compliance for you. You have options to typically integrate them via plugins for e commerce platforms or their APIs for custom sites just like yours.... The sites usually walks its client through the whole process so you don't have to worry much but choose a reputable one at that.. here's a list of few BTC payments process on GitHub.. But if you which to also go for altcoins then you can try out bitpay or CoinPayments those are the few reputable ones I can recommend for now...

I don't think there's any detailed guide on how to create your own cryptocurrency payment gateway/processor out there. Although if you're serious about it, you can start by reading this documentation https://developer.bitcoin.org/devguide/payment_processing.html. That list isn't complete though. BitPay (which you've mentioned) and Coinbase Commerce aren't in the list, even though they're fairly popular option.

I think the scale of the site you are trying to create a payment system for depends on how serious the payment system would be. Basically for a site as big as Amazon you you would be faced with a lot of things you would need to consider ranging from KYC and AML related problems. Nevertheless It also depends on if your site uses KYC or not too. Either way, make sure you don't store your keys to the receiving wallet on the web servers and ensure your payment channel is secure so you don't end up losing funds to a hacker.