Braintree assigns a certain number of processing terminals(through one of their partner banks) to each of its merchants for processing payment. 

This error indicates that there is a higher number of transactions to be processed than there are processing terminals in your account at a particular time. Error 3000 occurs when too many transactions are sent in for processing at exactly the same time and Braintree’s partner bank cannot handle them all together.

This response could also indicate a problem with the back-end processing network, not necessarily a problem with the payment method.

Solution:

To resolve this error, you can either contact Braintree for more processing terminals assigned to your account or ensure that individual transactions are processed at different times on the Chargebee interface.

Chargebee will consider this as a failed transaction and the payment will be retried as per your dunning settings.

Feel free to contact Chargebee support for more info.