I am having trouble calculating a unique ID the way you calculated. I’ve attached a screenshot here. Also, I was confused because in your attached sample file there are 3 rows of “now()”, so does KoBo take the last one?
In the above, the unique ID is not generating anything - the field appears blank after submitting.
Welcome to the community, @aahmed! Have you gone through our support article Creating Unique Serial Numbers in Forms? Besides, we also have a list of community discussions that have happened previously which should help you solve your issue.
Dear @Kal_Lam , thank you very much for pointing me to these, I shall go through them. Previously I had used “once(int(899999*random())+10000)”, and concat on multiple strings/numbers. I shall check out the other methods too, thank you! 
