PHP cURL request headers isn't working with a global variable - php

Question

I've set a global variable to equal an access token, and when I print_($session_id) the token is visible. What I'd like to do is pass that variable into my CURLOPT_HTTPHEADER, and have it equal to "Session" in the function get_field_data_id() below:
function get_session_id() {
global $session_id;
$curl = curl_init();
$session_url = "/auth";
curl_setopt_array($curl, array(
CURLOPT_URL => $session_url ,
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "GET",
CURLOPT_HTTPHEADER => array(
"Content-Type: application/json",
"Accept: application/json",
"username: USER",
"password: PASS",
"authorizationkey: KEY"
),
));
$response = curl_exec($curl);
curl_close($curl);
$session_id = $response;
} add_filter( 'gform_after_submission_4', 'get_session_id' );
function get_field_data_id() {
global $session_id;
$curl = curl_init();
$file_url = "URL";
curl_setopt_array($curl, array(
CURLOPT_URL => $file_url,
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 0,
CURLOPT_FOLLOWLOCATION => true,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "GET",
CURLOPT_HTTPHEADER => array(
"Content-Type: application/json",
"Accept: application/json",
"Session: {$session_id}"
),
));
$response = curl_exec($curl);
curl_close($curl);
echo $response;}
However when I run this function, I get an error message that the session ID is invalid. What am I missing?
{"Message":"Invalid Authorization. Session ID is invalid. "}