Your instance url looks like it is not a Jira cloud instance. By any chance are you running on a server deployment and not on cloud? If so, that explains the 404 since that REST API is not available in Jira server REST API.
Your instance url looks like it is not a Jira cloud instance. By any chance are you running on a server deployment and not on cloud? If so, that explains the 404 since that REST API is not available in Jira server REST API.