uses ..., fphttpclient, opensslsockets, ...
with TFPHTTPClient.Create(nil) do
try
AddHeader('Content-Type', 'application/json; charset=UTF-8');
AllowRedirect := True;
RequestBody := TStringStream.Create('{JSON}');
Memo.Lines.Add(Post('https://url'));
finally
RequestBody.Free;
Free;
end;