I have to generate unique random numbers in robot framework. I have used \"Generate Random String\" to get random numbers. Command:
${random} Generate Ran
I think you should try below code. It will give you a 4 digit unique random number from "0123456789"
library String
${PO_Number} Generate random string 4 0123456789
I hope it will work for you as it worked for me.
Regards, Arvind Kumar