Create Rule with valueType "Substring" via API

Hi everyone

I'm trying to create a Rule via the API. According to the documentation, the body needs to be provided as follows:

<rule xmlns="http://www.vmware.com/UM"><vcServerId>1</vcServerId><customerName>CustomerTest</customerName><objectType>VM</objectType><valueType>Unique ID</valueType><value>vm-21</value></rule>

This works fine for rules with valuetype "Unique ID". But i need to create a rule with the valuetype Substring and I cannot figure out, how I need to provide the body. If I send it according to the documentation i get the response that rules with valueType Substring mustn't provide a vCenter ID. If I send the body without the vcServerID Element i get the response that this is a mandatory element. If I leave it blank I get a parsing error back. Can anyone point me in the right direction? We use version 3.6.1.

Thanks!