ScriptRunner for Jira Cloud is able to execute rest calls to third-party rest API's and that the simplest way to test executing these calls would be to use the Script Console as described on the documentation page here which also contains some simple examples of how to execute rest API calls.
In order to get started with how integrating ScriptRunner for Jira Cloud with an external application then we would advise following the steps outlined below.
- Contact the support team for the external application to ask them to provide examples of how to use the Rest API for the external application.
- Locate the Rest API documentation for the external application.
- Start testing interacting with the Rest API's for the external application on the Script Console ensuring that Script Variables are used to store any passwords or authorization tokens.