Bad Request in QuickBooks API production, works in sandbox - php

Question

Today I tried to switch over development code to a limited-release production environment and immediately ran into issues.
The QuickBooks Accounting API works fine, however when it comes to payments I am able to accept them in sandbox mode but production returns "400 Bad Request"
I'm using my production API keys, I'm accessing the production API endpoints (api.intuit.com as opposed to sandbox.api.intuit.com), and I know the query I'm sending should be fine since it works in sandbox mode (unique Request-Id, amount, token, and currency provided in request body, proper content-type header, etc)
I also know my API key is fine since it works with the QuickBooks Accounting API. I am able to create a customer and create an invoice, but when I attempt to collect payment on the invoice it throws up on me.
What could be going wrong? I can post any code snippets or errors required. I'm using Laravel 5.2 with a phpOauthLib wrapper written by lusitanian.
The code I'm using:
$oauth = OAuth::consumer('QuickBooks');
$oauth_token = unserialize(file_get_contents(storage_path("tokens/oauth.token")));
$storage = $oauth->getStorage();
$storage->storeAccessToken('QuickBooks', $oauth_token['access_token']);
$member = Member::find(Request::get('id'));
$query = urlencode("select * from customer where displayname = '" . $member->first_name . " " . $member->last_name . "'");
$result = json_decode($oauth->request("/v3/company/" . $oauth_token['company_id'] . "/query?query=" . $query, "GET"));
$donor = null;
if( !property_exists( $result->QueryResponse, 'Customer' ) ) {
$donor = $oauth->request("/v3/company/" . $oauth_token['company_id'] . "/customer", "POST", json_encode([
'DisplayName' => $member->first_name . " " . $member->last_name
]), array('Content-Type' => 'application/json'));
} else {
$donor = $result->QueryResponse->Customer[0];
}
$pledge = $oauth->request("/v3/company/" . $oauth_token['company_id'] . "/invoice", "POST", json_encode([
'Line' => [
[
'Amount' => '25.00',
'DetailType' => 'SalesItemLineDetail',
'SalesItemLineDetail' => [
'ItemRef' => [
'value' => '21'
]
]
]
],
'CustomerRef' => [
'value' => $donor->Id
]
]), array('Content-Type' => 'application/json'));
$pledge = json_decode( $pledge )->Invoice;
$guid = GUID();
/************** THIS IS THE LINE THAT FAILS: ***************/
$capture = $oauth->request("https://api.intuit.com/quickbooks/v4/payments/charges", "POST", json_encode([
'amount' => $amount,
'token' => Request::get('token'),
'currency' => "USD"
]), ['Content-Type' => 'application/json', 'Request-Id' => $guid]);
$capture = json_decode( $capture );
$payment = $oauth->request("/v3/company/" . $oauth_token['company_id'] . "/payment", "POST", json_encode([
'CustomerRef' => [
'value' => $donor->Id,
'name' => $donor->DisplayName
],
'TotalAmt' => $capture->amount,
'Line' => [
[
'Amount' => $capture->amount,
'LinkedTxn' => [
[
'TxnId' => $pledge->Id,
'TxnType' => 'Invoice'
]
]
]
]
]), ['Content-Type' => 'application/json']);
Again, this code worked perfectly with the sandbox API, but now it fails. Tonight I'll see what I can do to get the HTTP transaction (request and response)