This article outlines the steps on how to resolve the JSON API Error that you might encounter when you are unable to send cases to spam.
When trying to send a case to spam, you might encounter the following error in the UI:
JSON API Error: Could not load /api/0/spam/
This error is the result of an encoding issue when FogBugz attempts to convert the sender's name from the email (in a non-standard encoding), causing the Correspondent field to show a lengthy value composed of gibberish characters. Because the name/value is too long, the Correspondent field doesn't show the sender's email address. FogBugz is unable to parse the field to add the email address to its auto sorting functionality.
To resolve the error:
Edit the case.
Remove the gibberish characters.
Change the content of the Correspondent field to the email address you can see from the incoming message/email.
FogBugz will be able to parse the field properly, and you can mark/close the message as spam.