curl --location --request POST '/rest/api/3/issueLink' \
--header 'Content-Type: application/json' \
--data-raw '{
    "comment": {
        "body": {
            "content": [
                {
                    "content": [
                        {
                            "text": "Linked related issue!",
                            "type": "text"
                        }
                    ],
                    "type": "paragraph"
                }
            ],
            "type": "doc",
            "version": 1
        },
        "visibility": {
            "identifier": "276f955c-63d7-42c8-9520-92d01dca0625",
            "type": "group",
            "value": "jira-software-users"
        }
    },
    "inwardIssue": {
        "key": "HSP-1"
    },
    "outwardIssue": {
        "key": "MKY-1"
    },
    "type": {
        "name": "Duplicate"
    }
}'