Thanks @Ha_Tr_n, how’s it going? Have you tried using the Request Signatures example:
$body = array(); // JSON body goes here. Always empty for GET;
// strip nonfunctional whitespace.
$body_string = json_encode($body);
Compared to:
$body = $request->all();
$bodyString = $body && !is_null($body) ? json_encode($body, JSON_UNESCAPED_SLASHES) : '';