Modal issues when cancelloing exiting a textbox

HI I have a userform with various textboxes in it. one textbox I want to only contain numbers so I have the following code trigger if a letter is entered

 If Not IsNumeric(supplierpricetxt.Value) Then

        MsgBox "Sorry, only numbers allowed"
         
         With supplierpricetxt
        .SelStart = 0
        .SelLength = Len(.Text)
         End With
        
        Cancel = True
Exit Sub
End If

This works fine when the property of the userform modal is set to true. the current textbox highlights the current text for me to overwrite. the problem is when I switch the userform to modal = false it doesn't work.

Any ideas why this is and whether there is a simple workaround.

Also the above code will allow eg 100 to be entered or £100. Is there a way to exclude the £100 being accepted.

thanks in advance and happy new year

hi here it is

Private Sub supplierpricetxt_Exit(ByVal Cancel As MSForms.ReturnBoolean)

  
 If Not IsNumeric(supplierpricetxt.Value) Then

        MsgBox "Sorry, only numbers allowed"
         
         With supplierpricetxt
        .SelStart = 0
        .SelLength = Len(.Text)
         End With
        
        Cancel = True
Exit Sub
End If