Forbidden, create payment error 403

Hello,
we are trying to execute a payment creation with PHP MATCH_CODE api call but we receive ERROR 403 with following payload:

data: { code: 45, message: 'Forbidden', wlt: 'S8joVKnO' } },

The php code that we have used is:
\SatispayGBusiness\Api::setSandbox(true);

\SatispayGBusiness\Api::setPublicKey($publicKey);
\SatispayGBusiness\Api::setPrivateKey($privateKey);
\SatispayGBusiness\Api::setKeyId($keyId);

$payment = \SatispayGBusiness\Payment::create([
"flow" => "MATCH_CODE",
"amount_unit" => $importo,
"currency" => "EUR",
"external_code" => "my_order_id",
"callback_url" => "/satispaypayment/test?prova=OK",
"metadata" => [
"order_id" => "1",
"user" => "00004",
"payment_id" => "1",
"session_id" => "my_session",
"key" => "value"
]
]);

Could you please help us understand what are we doing wrong?

Many thanks for kind attention and prompt answer