FIRSTNAME attribute on Brevo plugin form not getting saved with the contact

I have the brevo plugin on my wordpress website with two fields: email and name. Unfortunately, only the ’email’ is getting saved. Even after contacts are confirming the double opt-in, when I check them back on my brevo mailing list, the name they entered isn’t saved (and so any personalisation doesn’t work).

The code is as follows:

<p class="sib-email-area">
    Email Address*
    <input type="email" class="sib-email-area" name="email" required="required">
</p>
<p class="sib-FIRSTNAME-area"> 
    <label class="sib-FIRSTNAME-area">Your Name*</label> 
    <input type="text" class="sib-FIRSTNAME-area" name="FIRSTNAME" required="required"> 
</p>
<p>
    <input type="submit" class="sib-default-btn" value="Subscribe">
</p>
<p>Your e-mail address is only used to send you our newsletter and information about our activities. You can always use the unsubscribe link included in the newsletter.</p>