Dataplane add backend 400 error after 1 success

Hi im currently trying to use haproxy dataplane api to add backend servers.
It works once but im just getting err code 400 after the first attempt.

My command (only works the first time)

curl -X POST -H “Content-Type: application/json” --user {userParams} \ -d '{ "address": "'{address}’", “check”: “enabled”, “maxconn”: 1, “name”: "’{name}'", "port": '{port}’ }’

Is there a step im missing?