Are there any 3rd party APIs to find out who and how much has been paying a given address?
This data isn't anonymous in the blockchain ...
I need to step in here, cause I fear another discussion on loosing my privacy
I look into it from the perspective of help organizations (ONGs). In FIAT world, they usually get funds by foreign countries to their bank accounts. And in the country of operation, they meet conflicting goals. Some governance have then frozen their banking accounts. And I can't stress is importantly enough: THIS IS NOT A PROBLEM OF SMALL THIRD WORLD COUNTRIES! IT HAPPENS ALSO IN THE NORTHERN HEMISPHERE...
It is not the always repeated "tax avoiding" issue.
So, when you say "who", it's a question of defining what do you mean by "who"? Looking at block explorers (e.g. blockchain.info), they do exactly this, when it comes to bitcoin addresses and values. Even dates. So the "who" can be address x payed y bitcoins to address z at a specific date. This is anonymous data in the blockchain, and becomes pseudo anonymous, when it comes to real people. Chainanalysis has already been mentioned...
To avoid that people can link information between me as a person and a used bitcoin address, the concept of "single address usage" must be followed. Then all these analyzers don't make sense. They will work with probabilities, but still there's a lot to go... Personally it would be even better, to use mixers and different exchanges. When is mimble-wimble finally introduced into the bitcoin eco system?