Welcome to the RingCentral Community

Can you explain and show the params (remove sensitive info) when you call that API.

Are you looking for a solution to do this via an API? If so, you can use the Create Extension endpoint to create an extension. You can specify a specific site id (ignore other site params as shown in the API reference). To read your company sites info, make a GET request to the following endpoint

GET /restapi/v1.0/account/~/sites

I tried that and this is the error that I get.

{

"errorCode": "CMN-102",

"message": "Resource for parameter [extensionId] is not found",

"errors": [

{

"errorCode": "CMN-102",

"message": "Resource for parameter [extensionId] is not found",

"parameterName": "extensionId"

}

],

"parameterName": "extensionId"

}