Cannot add custom field in user tab?

Hello, I am trying to add a custom field in the user tab using the metakey USER_nickname but for some reason when I click confirm, the plugin page refreshes and no custom field has been added to the user tab. I tried different metakeys and it’s not working too, but when I go to another tab, like products, i can successfully add a custom field to this. I wonder what i’m doing wrong. I hope this gets noticed, thank you