Here is an example of the call I am making: 
crm.sdata({
entity: "worktypes",
where: "wktp_caption_code eq '" + workType + "'",
success: processRecords,
error: processError
});

The processError is getting triggered and I can see  the 403 error in Chrome devtools.

Have you seen what the exact call is using something like "Telerik Fiddler"?  Is you check with Postman to see whether the is problem with

1) The why the REST call is made from within  the browser

2) A problem with the way in which Sage CRM form the request

3) Or truly a problem with the server itself.