I thought I was getting quite well until I came to validate show if.
On my page I highlight the message.
In server behaviours, click the plus, select WA, select validation, select validation show if.
The Validation page appears, and the finger icon appears, but when I click the plus button or the display space below nothing happens.
As I mentioned previously when I found this problem I noticed the recordset for the NewUsed table had disappeared fro the SB panel. It happened again this time. I closed and reopened the page and the recordset reappeared.
I attach some details below.