Log errors in response to Sync requests

[JakePT]

Is your enhancement related to a problem? Please describe.
When the Sync page sends an AJAX request to sync, if the response is not valid JSON the apiFetch function catches an error when parsing the JSON an throws a generic error message. This can make debugging for customers somewhat more difficult.

Describe the solution you'd like
Replace apiFetch with a regular fetch() implementation and log error responses to the console when parsing JSON before throwing a generic error message.