because 'realname' is a required field as 'email' is
for example if you have named your field for the name as 'name' and not as 'realname' you can use derive_fields in your form like the following:
<input type="hidden" name="derive_fields" value="realname=name" />
or if you want to split your 'realname' into two input fields ie. in firstname and lastname:
<input type="hidden" name="derive_fields" value="realname=firstname+lastname" />
this line has to be added after your form tag, but i think this is clear anyway ...