public function calculateFormSignature(string $orderNumber, string $cart, string $amount, string $currency): string|false 	{ 		$corvusParameters = [ 			'amount' . $amount, 			'cart' . $cart, 			'currency' . $currency, 			'language' . $this->language, 			'order_number' . $orderNumber, 			'require_complete' . $this->require_complete, 			'store_id' . $this->store_id, 			'version' . $this->version, 		];  		// parameters must be in alphabetical order 		sort($corvusParameters); 		$sortedString = implode('', $corvusParameters);  		return hash_hmac('sha256', $sortedString, $this->secret_key); 	}