How can I send Pager Message

Yes you can send pager message. Remember that it is internal messages, meaning that you can only send from one extension to another extension within an account. Here is the sample code for C#

Create Internal Text Message

HTTP POST /restapi/v1.0/account/{accountId}/extension/{extensionId}/company-pager

using (var rc = new RestClient("clientID", "clientSecret", "serverURL"))
{
    await rc.Authorize("username", "extension", "password");
    var result = await rc.Restapi(apiVersion).Account(accountId).Extension(extensionId).CompanyPager().Post(createInternalTextMessageRequest);
}

• Parameter createInternalTextMessageRequest is of type CreateInternalTextMessageRequest
• result is of type GetMessageInfoResponse
• Parameter apiVersion is optional with default value v1.0
• Parameter accountId is optional with default value ~
• Parameter extensionId is optional with default value ~