Have you looked at the Linux Foundations (Formerly Google Project) under the nearly identical name ? https://github.com/a2aproject/A2A There are many sub projects for the various languages like Go, Python, etc

Edit: to be clear, A2A does not include payment functions but it has some projects close to it that look like it’s trying to solve the same thing. A2P comes to mind from Google: https://cloud.google.com/blog/products/ai-machine-learning/a...

Sounds a lot like coinpay https://coinpayportal.com crypto payments and escrow for agents