WP Simple Pay: Block Duplicate Email Addresses

/**

 * @link https://library.wpcode.com/snippet/ro8xmx35/

 */

add_action(

	'simpay_before_payment_create',

	/**

	 * @param \WP_REST_Request WordPress REST API request.

	 */

	function( $request ) {

		// Retrieve form values.

		$fields = $request->get_param( 'form_values' );

		$email = $fields['simpay_email'];

		// Search for customers based on email.

		$customers = \SimplePay\Core\API\Customers\all(

			array(

				'email' => $email,

			),

			array(

				'api_key' => simpay_get_secret_key(),

			)

		);

		if ( ! empty( $customers->data ) ) {

			throw new Exception( 'Sorry, you already have an account with us.');

		}

		// Payment can be created.

	}

);