Portal iview request context

Hi expert,

i want invoke a portal iview web dynpro abap from a http POST request.

i want pass to iview a custom parameter named VENDOR.

if i set in property "application parameter" VENDOR=<Request.vendor> and i call the iview from a http POST request occured a error:

"Exception in Sap Application Integrator : unable to process template VENDOR=<Request.vendor> because VENDOR in an invalid terminaly property of context Request".

If i use standard property (for example <Request.Port>) the application running (like here http://help.sap.com/saphelp_nw70ehp1/helpdata/en/36/5e3842134bad04e10000000a1550b0/content.htm).

How to modify the property of context request of my iview and add this parameter (like <Request.xyz> of help.sap) ?

Thanks and regards.

Filippo