If blocking an IP address via ApiBlock, with the "hidename" parameter set to true, the block is successful, but the block doesn't actually hide the IP address (IP addresses can't be hidden).
However, in the API response, it appears as though the block will hide the IP address:
"block": { "user": "4.3.2.1", "userID": 0, "expiry": "infinite", "id": 1605, "reason": "", "anononly": false, "nocreate": false, "autoblock": false, "noemail": false, "hidename": true, "allowusertalk": false, "watchuser": false, "partial": false, "pagerestrictions": null, "namespacerestrictions": null, "actionrestrictions": null }
Note: "hidename": true,.
The API response should report "hidename": false, if the block does not hide the target.