What is Proof of Service (Holochain)?

Proof of Service is a relatively rare consensus mechanism that is used on certain blockchain protocols such as Holochain. In the case of Holochain, Proof of Service does not function like a traditional blockchain consensus mechanism, because the distributed hash table (DHT) plays the primary role in achieving network consensus. In this scenario, the Proof-of-Service protocol is merely designed to ensure that once a peer-to-peer transaction is completed, then the agent providing the service automatically issues an invoice and receives payment.