I have three organisations OrgA, OrgB and OrgC, on the jira service management cloud I would like to make it so that in an it service management project the request types RT1, RT2 and RT3 are only visible (openable) by the customers in OrgA and the other RT, RT4, RT5 and RT6 are openable by all of them (OrgA, OrgB and OrgC). I am not sure how to configure Jira Service Management to achieve this behaviour. Can someone please help me?
You can't do that. All visible request types will be visible to all customers from all organizations included within the specific project. If you have different request types for different customers (orgs), then perhaps having different Service Desks would be the way to go.
Lastly, when you do create different JSM projects for your different org's customers on request types (the current workaround) to separate what request types can be utilized by each org (one project for one org), you should configure the "Customer permissions" to control the project visibility via the portal UI.
Best, Joseph Chung Yin
Jira/JSM Functional Lead, Global Infrastructure Applications Team