Add Subscribers To Email Sequence Using API

I want to be able to send selected subscribers to a specific email segment. I was able to get the following route to work, even though it is a GET route. I changed it to POST as follows which posts all subscribers into the segment. However, I want to be able to specify which subscribers to add. I have tried multiple ways and can't get it to work. Here's the modified route: https://mydomain.com/wp-json/fluent-crm/v2/sequences/119/subscribers

Can someone smarter than me help?