Is the connection coming from the App Host, not sure if someone migrated the app from the Console, but the App Host might not have line of sight. You might also want to confirm if the Auth Token used for the app isn't expired. Typically, you can just CURL from the appliance where the app is running and add your proxy to the curl.
curl -x http://PROXY-TEST-FWIP:2799 api.xforce.ibmcloud.com
Note: If you are using a hostname here ^^, make sure you confirm it resolves or substitute in the IP to confirm the CURL connects.
If you don't have a proxy, try a simple CURL to confirm if you can connect, for example:
curl -v https://api.xforce.ibmcloud.com/lang
Other....
Has anyone regenerated the API key on the X-Force side of things as that might cause connections to not connect as expected? Also, if the API being used on the X-Force Exchange is not the same as assigned to the Watson account, then you can get 'Inactive Subscription' or 'Limits Error' in the UI. However, I would assume that since you cannot hit the API, then you might be experiencing a proxy issue.
If you are still stuck, I'd recommend a support case so someone can refer to the app log.
------------------------------
Jonathan Pechta
QRadar Support Content Lead
Support forums: ibm.biz/qradarforums
jonathan.pechta1@ibm.com------------------------------