To update an existing schedule see below for JSON and JSONAPI example.

NOTE: Remember to substitute the token (after Bearer) and the service id (the "69" below) to your own token and service id.

JSON:

curl -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE1MDE2ODg3NTMsInN1YiI6MX0.oLh_7lsktvX4NP-6Dh4ptGKZe6JEfzeMIgzDjRpMyHM"
-H "Content-Type: application/json" 
-H "Accept: application/json"
-X PATCH
-d "{\"interval\": 3}"
https://api.myrapidi.com/api/v2/service/69/schedules/19

The out-put for this example would be: 

{
  "code": "G_TEST22_NAV356001",
  "description": "Group TEST22 NAV356001", 
  "transfer": "", 
  "group": "TEST22", 
  "interval": 3, 
  "interval_unit": "Hours", 
  "status": "Stopped",
  "error_handling": "Skip",
  "last_datetime": null,
  "next_datetime": "2015-10-01T00:00:00Z",
  "error_interval": 0,
  "error_interval_unit": "Hours",
  "notify_interval": 0, 
  "notify_interval_unit": "Hours",
  "notify_datetime": null,
  "start_time": "00:00:00Z", 
  "end_time": "00:00:00Z",
  "monday": true, 
  "tuesday": true, 
  "wednesday": true,
  "thursday": true,
  "friday": true,
  "saturday": true, 
  "sunday": true,
  "tags": [
    {
      "code": "NAV300", 
      "value": "NAV356001"
    }
  ],
  "comments": [
  
  ] 

JSONAPI:

curl -H "Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE1MDE2ODg3NTMsInN1YiI6MX0.oLh_7lsktvX4NP-6Dh4ptGKZe6JEfzeMIgzDjRpMyHM"
-H "Content-Type: application/vnd.api+json" 
-H "Accept: application/vnd.api+json"
-X PATCH
-d "{\"data\":{\"type\":\"schedules\",\"attributes\": {\"interval\": 33} }}"
https://api.myrapidi.com/api/v2/service/69/schedules/19

The out-put for this example would be: 

{
  "data":{
    "id":"19",
    "type": "schedules",
    "attributes":{
      "code": "G_TEST22_NAV356001",
      "description": "Group TEST22 NAV356001", 
      "transfer": "", 
      "group": "TEST22", 
      "interval": 33, 
      "interval_unit": "Day", 
      "status": "Stopped",
      "error_handling": "Skip",
      "last_datetime": null,
      "next_datetime": "2015-10-01T00:00:00Z",
      "error_interval": 0,
      "error_interval_unit": "Hours",
      "notify_interval": 0, 
      "notify_interval_unit": "Hours",
      "notify_datetime": null,
      "start_time": "00:00:00Z", 
      "end_time": "00:00:00Z",
      "monday": true, 
      "tuesday": true, 
      "wednesday": true,
      "thursday": true,
      "friday": true,
      "saturday": true, 
      "sunday": true
    },
    "relationships": {
      "tags": {
        "data": [
          {
            "id": "7", 
            "type": "schedule_tags"
          }
        ]
      },
    "comments": {
      "data": [
  
      ] 
    }
  }
},
"included": [
  {
    "id": "7",
    "type": "schedule_tags",
    "attributes": {
      "code": "NAV300",
      "value": "NAV356001"
    }
  }
]