AS3 pool members using a list

Try removing the square brackets and quotes around the ${MEMBERS} variable in the JSON. I spotted this example from one of Sebastian_Maniak 's guides:

in the module:
    MY_POOLMEMBERS = jsonencode(var.pool_members)

in the json:
          "members": [{
            "servicePort": 80,
            "shareNodes": true,
            "serverAddresses": ${MY_POOLMEMBERS}
          }]