Indy 10 in Lazarus RingCentral API RingOut TIdHTTP - indy

Question

Lazarus 1.8.4
Indy 10 (March 2020)
Windows Server 2016
I'm trying to build a little "Dialer" module for a contact list I've built in Lazarus. After fiddling for months, I was finally able to translate all the RingCentral API settings into Postman, then into Indy HTTP settings, to accomplish obtaining a token. That part works reliably. However, I am unable to do a RingOut API. I always get 404 not found. The examples in other programming languages given by RingCentral in their docs don't translate well into Indy.
if htpCall.Connected then
htpCall.Request.Connection := 'close'; // Close the socket after using it to obtain the token
htpCall.Request.Clear;
htpCall.Request.Accept := 'application/json';
htpCall.Request.ContentType := 'application/json';
htpCall.Request.Username := '<redacted>'; // Client ID
htpCall.Request.Password := '<redacted>'; // Client Secret
htpCall.Request.CustomHeaders.Clear;
htpCall.Request.CustomHeaders.FoldLines := False;
htpCall.Request.BasicAuthentication := False;
htpCall.Request.CustomHeaders.AddValue('Authorization', 'Bearer ' + acc_tkn);
prms_lst.Add('from=<redacted>');
prms_lst.Add('to=<redacted>');
prms_lst.Add('callerId=<redacted>');
prms_lst.Add('country=Canada');
prms_lst.Add('playPrompt=true');
// Remove the text ".devtest" for the production version of your code, and replace the phone account with the real main phone number
htpCall.Post('https://platform.devtest.ringcentral.com/restapi/v1.0/account/<redacted>/extension/101/ring-out', prms_lst);
UPDATE:
If I leave the TIdHTTP open, then run the code above, I get a different error.
Sent:
POST /restapi/v1.0/account//extension/101/ring-out HTTP/1.1
Content-Type: application/json
Content-Length: 82
Authorization: Basic
Host: platform.devtest.ringcentral.com
Accept: application/json
User-Agent: Mozilla/3.0 (compatible; Indy Library)
from=&to=&callerId=&country=Canada&playPrompt=true
Rcvd:
HTTP/1.1 401 Unauthorized
Server: nginx
Date: Tue, 25 Aug 2020 01:50:24 GMT
Content-Type: application/json
Content-Length: 175
Connection: keep-alive
WWW-Authenticate: Bearer realm="RingCentral REST API"
RCRequestId: 57c97008-e675-11ea-87cf-005056bb81b6
{
"errorCode" : "AGW-402",
"message" : "Invalid Authorization header",
"errors" : [ {
"errorCode" : "AGW-402",
"message" : "Invalid Authorization header"
} ]
}