You have added a second API Appliance to your Enforce Server, and have followed the documentation for configuring your Client.
However, requests for the second Appliance are returning an error:
"Missing request header 'X-SYMC-DLP-DetectorID' for method parameter of type String"
This detail was not required for the first Appliance.
There was a defect in the 15.5 GA release, which required this information when more than one Appliance was present.
Release : 15.5 GA
Component : DLP API Appliance
Update the Appliance to the 15.5 MP1 release.
This patch is available at the main portal for software downloads, under the section marked "DLP15.5MP1Appliance ":
Details confirmed in the 15.5 MP1 Release Notes:
4225918 = The API Detection Appliance erroneously required the HTTP header X-SYMC-DLP-DetectorID