Symptoms

1. Entering the linkedIssues(ISSUE-ID) results to the following which is VALID since the JQL is already showing the  [ x ] icon:

2. Entering the linkedIssues is (ISSUE-ID) results to the following:

Cause

Wrong parameter is used for the Advanced Search. 

Workaround

Instead of using those 2 JQL, please use the following instead:

As mentioned in the Examples that were provided and also it is mentioned that the Supported Fields is actually issue from the documentation:

• Find issues that are linked to a particular issue:

  issue in linkedIssues(ABC-123)

• Find issues that are linked to a particular issue via a particular type of link:

  issue in linkedIssues(ABC-123,"is duplicated by")

Please make sure that you have the issue field present in the parameter of the JQL