I am. Relating an app for a company. The app can capture up to 8 devices per user. In each device, I have a column called "Serial number/Barcode ", this is the column used to identify that device, and only that device because serial number /Barcode are specific to one device.
when I enter a serial number /Barcode that has already been entered I want the app to reject it, and shows an error message, to try to achieve this, I used the Valid_if, with the expression [_THIS] <>[Serial Number /Barcode device 2], and I repeated this expression for 6 other devices, I added all these expressions in the serial number /Barcode of the first device in the Valid_if,
. But the expre is not working