Segmentation is achieved by adding a contact filter to a campaign draft resource using the property SegmentationID. $ID_CONTACT_FILTER is the ID of the contact filter that you have created.
# Create : Newsletter data with segmentation.
curl -s \
-X POST \
--user "$MJ_APIKEY_PUBLIC:$MJ_APIKEY_PRIVATE" \
https://api.mailjet.com/v3/REST/newsletter \
-H 'Content-Type: application/json' \
-d '{
"Title":"Mailjet greets every contact over 40",
"Locale":"en_US",
"Sender":"MisterMailjet",
"SenderEmail":"Mister@mailjet.com",
"Subject":"Greetings from Mailjet",
"ContactsListID":"$ID_CONTACTLIST",
"SegmentationID":"$ID_CONTACT_FILTER"
}'