Error at node etl-demo/etl.js

[Jero2760]

Trying to follow this demo from Curatr course, with my own Learning Locker installation, End point and Auth, I get this error:
UnhandledPromiseRejectionWarning: FetchError: invalid json response body at http://my_ec2_url/data/xAPI reason: Unexpected token < in JSON at position 0
Could you help me with this?