Auth error when trying to make a transaction

When adding the basic example code to my Laravel project I keep getting this error

I'm generating the auth token on the server-side, sending it to the client and all the fields are working. When trying to execute a transaction()->sale() on the server-side I get the above error

$gateway = new Braintree\Gateway([
    'environment' => config('services.braintree.environment'),
    'merchantId'  => config('services.braintree.merchantId'),
    'publicKey'   => config('services.braintree.publicKey'),
    'privateKey'  => config('services.braintree.privateKey')
]);

$result = $gateway->transaction()->sale([
    'amount' => '5.99',
    'paymentMethodNonce' => $request->get('nonce'),
  ]);

The credentials are also correct because I can create a customer but not a transaction

Thanks

braintree / braintree_php

Auth error when trying to make a transaction #291