Swimlanes.io is a free webapp for making sequence diagrams. You simply edit the text on the left and the diagram is updated in real time. You can download your sequence diagrams as images or distribute with a link.
title: Scenario 4 Mobile/Web App -> TrustingSocial Server: Call services OCR, Face Matching, Liveness, Tampering,... Mobile/Web App <- TrustingSocial Server: Return eKYC result