It is possible that your store is password protected or similar.
So you would need to try the following:
white-list "app.dragdropr.com" server IP address "136.144.128.56" so that it can communicate with the Magento store using rest API.
the rest API route needs to be working: "{magento1-url}/api/rest"
the m1 server should not strip "Authorization" header
Reach us in case of any questions:)