Why do restaurants need to enter bank details if this doesn’t cost anything?

This article explains why restaurants are asked to provide bank details.

Restaurants are being asked to provide bank details only so that they can accrue their diners’ £1.23 contributions over the month and send it to Sustainably Run.

Contribution amounts are counted in the background by the restaurant's EPOS company, and the amount collected by Direct Debit will solely be for the contribution amounts.

Customers should be advised to make sure they see these payments as separate to their usual takings or profits.