If you wish to see if emails are being opened by their recipients it’s enough to put {{ open_tracking }} token anywhere in the message. It could be sent with the API call or be a part of message template.

This token gets replaced with a 1x1 pixel transparent image.

Make sure it’s in the HTML part of an email message. The caveat is that the recipient must enable images viewing for this tracking to work.

Then you can see if email was opened or not: