The 701 error with HTTP status 500 means the requestURL is not valid. Therefore, check the endpoint you are sending the request to.
Also, this can occur if you are trying to do a 3DS2 transaction and the endpoint version you are pointing to doesn't support 3DS2 yet.
How to solve this depends on your integration:
If you are using our Checkout API (endpoint: https://checkout-test.adyen.com/v46/payments) we recommend upgrading to versions v46 or above.
If you are using the Classic Adyen API (endpoint: https://pal-test.adyen.com/pal/servlet/Payment/v46/authorise) we recommend upgrading to versions v46 or above.
Note that you will already be able to support 3DS2 if you are able to support redirect-based authentication. Take a look at our 3D Secure authentication documentation for guidance on this!