We can update a JIRA ticket with comments using the following comments in servicenow. Here is example below:

Host : JIRA Website (https://spssweb1.atlassian.net)

Endpoint: host/rest/api/2/issue/SPSSWEB-1/comment

header: ‘Content-Type: application/json’

Credentials: https://snowexpertrohit.com/jira/create-basic-creadetials-in-jira/

SPSSWEB-1 – is the task key.

Body:

{
    "body": "Testing from ServiceNow"
}