What is the correct way to create a custom action using REST API in SharePoint Online?

Question

I'm trying to use Microsoft Flow and the Send an HTTP request to SharePoint action to deploy an SPFx application customizer to a modern team site.

I'm able to use the /_api/Site/UserCustomActions endpoint to list existing custom actions but keep getting errors when I try to create new using REST

Site address: https://contoso.sharepoint.com/sites/a-modern-team-site

Method: POST

Uri: /_api/Site/UserCustomActions

Headers:

• Accept application/json; odata=verbose
• Content-Type application/json; odata=verbose

Body:

{
    '__metadata': { 'type': 'SP.UserCustomAction' },
    "Location":"ClientSideExtension.ApplicationCustomizer",
    "Rights":"ManageWeb",
    "Title":"EnableTeamsApplicationCustomizer",
    "Name":"EnableTeamsApplicationCustomizer",  
    "ClientSideComponentId":"fa80f680-bda9-4c15-a8fe-4e86be0bf593", 
    "ClientSideComponentProperties":"{\"autoCreate\":\"true\"}"
}

Here's the error I keep getting. I have tried various encoding of the client side properties, omitted it, but no results. I have tried different variations of the http headers, both with odata=verbose and odata=nometadata. I keep getting the same error, but can't find anything explaining the error.

{
  "status": 400,
  "message": "An unexpected 'PrimitiveValue' node was found when reading from the JSON reader. A 'StartObject' node was expected.\r\nclientRequestId: 43c303e3-4722-4b5e-a5b5-5fbcc686ec50\r\nserviceRequestId: 1b1e6c9e-a0a1-5000-f082-74dd369cc50f",
  "source": "https://contoso.sharepoint.com/sites/a-modern-team-site/_api/Site/UserCustomActions",
  "errors": [
    "-1",
    "Microsoft.SharePoint.Client.InvalidClientQueryException"
  ]

}

Answer 1

I finally figured out what was wrong. The "Rights" property doesn't take a string like "ManageWeb" but is an object with High and Low properties.

I had to either remove the property or define the High and Low permission mask bits.