The best way to get the payload will be to publish the generator using chrome and then copying the payload from developer console (F12).
For example:
Generator with variables<Please see attached file for image>
Publish to target<Please see attached file for image>
Capture the traffic
<Please see attached file for image>

Below is the Payload for the request
{
"name": "Publish_TEST_GEN1",
"description": "Publish to TEST using GEN1",
"projectId": 2352,
"versionId": 2353,
"type": "PUBLISHJOB",
"origin": "generation",
"scheduledTime": 1531496360001,
"jobs": [],
"parameters": {
"variableDefaults": [{
"name": "ADD",
"value": "ADD"
},
{
"name": "CITY",
"value": "CITY"
},
{
"name": "FIRSTNAME",
"value": "FIRSTNAME"
},
{
"name": "ID",
"value": "10"
},
{
"name": "LASTNAME",
"value": "LASTNAME"
}],
"generatorId": 2357,
"jobType": "PUBLISH",
"title": "Publish to TEST using GEN1",
"publishTo": "TGT",
"repeatCount": "1",
"tables": [{
"tableNo": 1,
"tableName": "Persons",
"status": 1,
"fileId": null
}],
"actionOnDuplicate": "exit",
"actionOnGenDuplicate": "exit",
"target": "dbo",
"dataTargetProfile": "TEST",
"dataSourceProfile": ""
}
}