Exception:

[
    {
        "message": "This feature is not currently enabled for this user.",
        "errorCode": "FUNCTIONALITY_NOT_ENABLED"
    }
]

Resolution:

This exception is thrown in Salesforce when the API Integration user is missing the required permission to complete the actions.

For Example, I faced this exception when I tried to retrieve Conversation Entries using an Integration User and the user didn’t had “Access Conversation Entries” permission.

https://infallibletechie2-dev-ed.develop.my.salesforce.com/services/data/v60.0/connect/conversation/8b76ae70-c528-4c00-bb2c-fcc36fd7bf1e/entries

“Access Conversation Entries” permission is required to retrieve or export Conversation Entries. After granting the “Access Conversation Entries” permission to the API Integration user, the issue was resolved.