email form: input field for mail does not appear?

I try to insert an Icegram popup for newsletter subscription.
My problem: the input field for email address does not appear on website, when the name is data[email] (which is necessary for MailPoet). When I take another name, the input field appears.

…other names with data[] are no problem, for example name field name=”data[form_field_ZTU1NmJhZmMxZTY5X2xhc3RfbmFtZQ==]”.

What’s the problem here and how can I solve that??