CF7 submission gets added to MailChimp without tag

This is my CF7 code. It successfully adds new subscribers to MailChimp perfectly! But it does not add the tag to MailChimp. I am using “TestTag” as the tag for troubleshooting. I created the tag TestTag in my MailChimp account but that didn’t help. I am using a unique email address for every submission I do so every submission is a new subscriber. What is wrong? I don’t see any settings for tags in the plugin itself. I am using the free version of MC4WP with a wordpress.com website on the business plan. I first installed both plugins a few days ago and they are up to date.

<label> First Name (required)
    [text* mc4wp-FNAME]
</label>

<label> Middle Name (required)
    [text* mc4wp-MNAME]
</label>

<label> Last Name (required)
    [text* mc4wp-LNAME]
</label>

<label> Email (required)
    [email* mc4wp-EMAIL]
</label>

<input type="hidden" name="mc4wp-subscribe" value="1" />
<input type="hidden" name="mc4wp_tags" value="TestTag" />

[submit "Submit"]