Error: You must add the private key file Fatal Error

ive got a Problem with the plugin version 2.1.0 after enable i get a massage Error: You must add the private key file, website is now not available. what is the Porblem
error File:

2022-01-21T08:45:27+00:00 CRITICAL Uncaught Exception: Unable to load file:  in /pages/95/45/d0015674/home/htdocs/metal_earth/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/vendor/amzn/amazon-pay-api-sdk-php/Amazon/Pay/API/Client.php:412
Stack trace:
#0 /pages/95/45/d0015674/home/htdocs/metal_earth/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/vendor/amzn/amazon-pay-api-sdk-php/Amazon/Pay/API/Client.php(379): Amazon\Pay\API\Client->setupRSA()
#1 /pages/95/45/d0015674/home/htdocs/metal_earth/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/includes/class-wc-amazon-payments-advanced-api.php(403): Amazon\Pay\API\Client->generateButtonSignature('{"storeId":"amz...')
#2 /pages/95/45/d0015674/home/htdocs/metal_earth/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/includes/class-wc-gateway-amazon-payments-advanced.php(169): WC_Amazon_Payments_Advanced_API::get_create_checkout_session_config()
#3 /pages/95/45/d0015674/home/htdocs/metal_earth/wp-includes/class-wp-hook.php(303): WC_Gatewa in /pages/95/45/d0015674/home/htdocs/metal_earth/wp-content/plugins/woocommerce-gateway-amazon-payments-advanced/vendor/amzn/amazon-pay-api-sdk-php/Amazon/Pay/API/Client.php in Zeile 412

Chris

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