Rest support

for single field:

#!js

{"update":{
  "customfield_xxxxx": [{
    "set": {"name": "OptionName"} // or {"id": "optionId"} // or {"name": "path/to/OptionName"}
  }]
}}

for multi field

#!js

{"update":{
  "customfield_xxxxx": [{
    "set": [
       {"name": "OptionName1"}, // or {"id": "optionId"} // or {"name": "path/to/OptionName"}
       {"name": "OptionName2"}
     ]
  }]
}}

{"update":{
  "customfield_xxxxx": [{
    "add": {"name": "OptionName"} // or {"id": "optionId"}
  }]
}}

{"update":{
  "customfield_xxxxx": [{
    "remove": {"name": "OptionName"} // or {"id": "optionId"}
  }]
}}

Create issue ex:

#!js

{
  "fields": {
    "project": {
      "id": "XXXXX" 
    },
    "issuetype": {
      "id": "XXXXX"
    },
    "summary": "New issue ",
    "customfield_XXXXX": { // Sinle choice
      "name": "path/to/OptionName" // or {"id": "optionId"}
    },
    "customfield_XXXXX": [ // Multiple choice
      {"name": "path/to/OptionName"},
      {"name": "path/to/OptionName2"}
    ]
  }
}

for admin use Atlassian REST API Browser plugin marketplace

Wiki

tree-customfield / Rest operations

Rest support