verify the length of a value in the header

Here's what you can do, I've tested it, able to capture it fine.

    set digits [findstr [HTTP::payload] "<singleValue>" 13 "<"]
    log local0. "$digits & legth is [string length $digits]"

Payload:

<values>
<name>operatorUserId</name> 
<singleValue>1234567809</singleValue> 
</values> 

Output:

<HTTP_REQUEST>: 1234567809 & legth is 10

Payload:

<values>
<name>operatorUserId</name> 
<singleValue>1234567</singleValue> 
</values> 

Output:

<HTTP_REQUEST>: 1234567 & legth is 7

Now with the length value, you can either set it on a variable and do a if condition and send to respective virtual. Hope it helps.