/*
* This example script  console script updates a watcher on an issue.
* "All right, title and interest in this code snippet shall remain the exclusive intellectual property of Adaptavist Group Ltd and its affiliates. Customers with a valid ScriptRunner
* license shall be granted a  non-exclusive, non-transferable, freely revocable right to use this code snippet only within their own instance of Atlassian products. This licensing notice cannot be removed or
* amended and must be included in any circumstances where the code snippet is shared by You or a third party." 
*/

// Specify the key of the issue to add below
def issueKey = "<IssueKeyHere>"

// Add the account ID of the user to add as the watcher below as this will define the user in the collection format that the watchers field requires. 
// Note as the watcher field is a collection you can specify a comma seperated list of account ID's to add more than one user as a watcher.
["<accountIdHere>"].each { accountId ->

// Make the rest call to update the issue and set the watcher using the *accountID* provided for the user.
def result = post('/rest/api/2/issue/' + issueKey + '/watchers')
.header('Content-Type', 'application/json')
.body("\"${accountId}\"")
.asString()

}