get https://marketplace.walmartapis.com/v3/shipping/labels/carriers//trackings/
This API retrieves label for a carrier & tracking number combination.The response to a successful call contains the tracking number with the pdf or image type based on the media type passed in Accept header.
For eg. 'Accept'='application/json,application/pdf' will result in pdf media type and
'Accept'='application/json,image/png' as image media type.