I just signed up for the Monzo Beta in USA. I found the labeling in the sign up flow to be a little confusing, specifically the copy in the Name field.
The copy for the default text for the field is “Full legal name” and the copy for the label below the field is “Add preferred name” (see screen grab: https://d.pr/i/FyyfU5)
I’d guess that for many people, these are not the same thing. For example, someone might be legally named “Jeffery Fontleroy Douggins” but preferred to called “Jeffey Doug”