This is to be expected when the Shield Firewall is active. It's designed to, based on the rules you choose, block requests that match certain patterns.
If you're having trouble with this and it is blocking legitimate requests to your site from 3rd party services, then you have 2 options:
1) Remove the particular Firewall check that is blocking the important request
2) Whitelist the page/parameter that is receiving the request
First, you need to find the block
So before you can do anything you need to know what's blocking your important requests. To do this:
- Enable the Audit Trail module (if it isn't already)
- Ensure that the option for auditing for the Shield plugin is enabled
- Simulate the important request
- Go immediately to the Audit Trail Viewer
Once you have the request captured in the Audit Trail, the entry will tell you exactly the parameter that was blocked, and the Firewall rule that blocked it
Second, unblock all future requests
Now that you have the parameter and the rule, you can pick whichever option from the list above your prefer.
1) Go to the Firewall module and disable the option that corresponds to the firewall rule that is found to be blocking your important requests;
2) Go to the Firewall module and open the 'whitelist' tab. In the text box for white listing parameters, enter the following line (where "name_of_your_parameter" is the name of the parameter that you discovered was blocked and want to ensure never gets blocked)
Now simulate your important response and review the Audit Trail to ensure it's not being blocked.