It is useless for online activation. However, you can use it as a "password" for some offline cracks. Look for a "Manual Activation" button. If the game offers an offline HTML file activation, use your real key to generate a response file using the method in Step 2.
If those avenues don't provide a solution, and you're still interested in trying the "activation key fix", please ensure you: Bad Piggies 1.5.1 Activation Key Fix
: Intercepts the game's outgoing server request and sends back a "simulated" success response, tricking the game into thinking it has been officially activated. It is useless for online activation