As an alternative to PayPal I think NexusMods should add cryptocurrency option as a method to donate to mod authors. And I know it won't be hard to add this feature to the website since no API will be needed.
How it will work is that an author can add/remove a cryptocurrency wallet to their account. To add one they will need to give the wallet a name such as Bitcoin, Ethereum, Litecoin. Then they will need to paste the wallet address and then click save. Then when someone downloads a file from the mod author or views their profile they will see a list of wallet addresses they can send crypto to.
No need for an API, all that is needed is a form to be made and a database to store the wallet names and addresses.
The best with this is there are hundreds of cryptocurrencies and you can add anyone of them to your account an accept donations in that currency.