Can I set in the system the 3% charge when the guest pays by card? / How to add surcharge for any payment type in eZee Absolute?

To set surcharges, you need to login into Configuration >> Master >> General >> Pay Method >> Edit payment type which you want to add surcharges.

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To add surcharges on payment type, select one of the extra charges to post surcharges, create one extra charge as Surcharges.