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What are smart routing rules?
How to configure my default gateway?
You are seeing this error because you do not have a gateway assigned for the particular currency (based on the plan).
Smart Routing Rules, allows you to configure which gateway will be used by default when you have multiple gateways for the same payment methods/currency. Eg, 2 Stripe or 2 GoCardless accounts configured in Chargebee.
It is recommended to configure default gateways for each payment method and currency.
All you need to do is go to; Settings » Configure Chargebee » Payment Gateways » Manage Rules » Select Gateway against Currency & Payment Type
If you have any further questions, please reach out to firstname.lastname@example.org.