contingency: VALIDATION_ERROR , while proceeding with Subscribe Button.

[sudhansh]

I am creating a subscription flow for a product plan. 
All the subscription process is done by REST APIs.
But at the time when i proceed to subscribe after clicking `Login to subscribe button`, i am facing an error at the redirected page

with message Things don't appear to be working at the moment. Please try again later.

page URL is : https://www.sandbox.paypal.com/webapps/billing/subscriptions?ba_token=BA-6RL60762NP651641S

In console it gives error:

1. Request URL:
   https://www.sandbox.paypal.com/webapps/billing/api/billagmt/BA-6RL60762NP651641S/createCart
2. Request Method:
   POST
3. Status Code:
   400 Bad Request

with response : 

{"ack":"contingency","contingency":"VALIDATION_ERROR","meta":{"calc":"......","rlog":"......"},"server":"......."}​

What is the real problem here?

[guikubivan]

Getting this issue when testing a live setup. Could it be PayPal locks you out if you test too much?

[bethmarlatt]

Same- both in live and sandbox subscription mode