SimpleIssueCustomField vs SimpleProjectCustomField Follow

I am trying to follow guide in docs: https://www.jetbrains.com/help/youtrack/standalone/api-howto-create-issue-with-fields.html

I am stuck at step 2: "Obtain the name and $type of the custom field that you need to set. You can send a GET request to the /api/issues endpoint with query parameters".

I don't understand why you are supposed to read an issue when you want to create a new one. For example, my project have no issues, and I want to create one via API. /api/issues will return an empty set. Now what?

I tried to call /api/admin/projects/TEST/customFields instead. This works, but returned $type is SimpleProjectCustomField. Attempt to create an issue: 

{
  "project":{
    "id":"0-0"
  },
  "summary":"Test",
  "description":"Test",
  "customFields":[
    {
      "name":"Test",
      "value":1,
      "$type":"SimpleProjectCustomField"
    }
  ]
}

will fail with:

HTTP Error 500: (HTTP_STATUS_SERVER_ERROR) class jetbrains.charisma.customfields.simple.common.SimpleProjectCustomFieldMegaProxy cannot be cast to class jetbrains.charisma.persistence.customfields.IssueCustomField (jetbrains.charisma.customfields.simple.common.SimpleProjectCustomFieldMegaProxy and jetbrains.charisma.persistence.customfields.IssueCustomField are in unnamed module of loader org.eclipse.jetty.webapp.WebAppClassLoader @20e3dc94)

However, if I manually replace SimpleProjectCustomField with SimpleIssueCustomField:

{
  "project":{
    "id":"0-0"
  },
  "summary":"Test",
  "description":"Test",
  "customFields":[
    {
      "name":"Test",
      "value":1,
      "$type":"SimpleIssueCustomField"
    }
  ]
}

Then this will be executed without a problem.

What am I missing? How do I obtain the "proper" $type?