A study by Baymard reveals that 89% of users tend to enter numerical inputs in several different ways even if the placeholder shows the formatting example.^[1]

To prevent validation errors, use input masks when proper formatting matters (such as with phone numbers or dates). It not only displays the desired input format but also auto-applies the input as users are typing. It reduces cognitive load and confusion, so users don't need to worry and double-check if the phone number is valid when they enter "+" or use parenthesis "()."