Verified on staging.apinf.io

API with correct Swagger specification but there doesn't display Swagger UI because URLs are not available and there throws error

{  
  "code":"ECONNREFUSED",
  "errno":"ECONNREFUSED",
  "syscall":"connect",
  "address":"172.18.0.2",
  "port":443,
  "name":"Error",
  "message":"Error downloading file "https://staging.apinf.io/rest/v1/catalog.json" 
connect ECONNREFUSED 172.18.0.2:443",
 }

The first look shew that the problem came from the staging.apinf.io networking.

How to check
The command curl -I https://staging.apinf.io/rest/v1/catalog.jsonreturns the error inside of Docker container