Q:

What could be the reason of Bing API key not working? 

I have been trying to work with Bing API to make a custom search engine.  I obtained a free Bing Search API which work perfectly when I tried to use it using azure marketplace website.  But wheneever I tried using it the URL like
http://api.bing.net/json.aspx?Appid=m/gNRFAX3faTfrm+81uVSTHPJkf/Dimn2DTM7NyukpU=&query=sushi&sources=web. 
I get error saying 
Parameter has invalid value. 

So I tried using JavaScript and PHP same error accompanies every time.  Any idea why it is happening? 
Note: I did not put my original API key here. 

A:

Actually that API using the parameter AppId is deprecated.  You have to use azure bing API.  Use access token as value or client key.  Please look at this link. 
Hope this helps.