"Type Error : Failed to Fetch" While Testing on Developers Portal

In the process of testing an API on TYK developers portal, I encountered the below error:
“Type Error : Failed to Fetch”. While trying to fix the error, I used this link which I found on the community forum: "TypeError: Failed to fetch" for valid response.
In the definition file, I enabled CORS and set options_passthrough to true. But the error still persist.
Kindly assist.