Personalisation link to url with dynamic values in invoice workbench

Hi,

I am trying to do a personalisation to launch an URL with dynamic values from the invoice workbench. The dynamic value that I am trying to use is voucher number, which is found in voucher_num_display. I have tried the below but it is not working.

 

http://...the url… /default.aspx?SearchURL=true&EntID=1&ProjID=351&IndexFields=Voucher+Number&IndexValues="${item.inv_sum_folder.voucher_num_display.value}"&SortBy=Date&SearchType=And&ResultsType=Docs

 

Have I done this part correctly?

 

IndexValues="${item.inv_sum_folder.voucher_num_display.value}"

 

(it works if I hard code the voucher number in just not working dynamically).