manually generated uniqueid() - app sheet not allowing to be a key

[victorfarinella]

Hello everyone, how are you?

I'm trying to change the key of my spreadsheet that already have some data in it. So I followed the tutorial to use the spreadsheet formula:

But on appsheet, when I try to select it as key, instead of the row number, and save, the system changes back to the row number:

Does anyone know what is happening? 

Thank's!