They can send cryptocurrency to these addresses and it will be automatically exchanged into Euro or other fiat currency of your choice.
Primarily the premise of a channel is the customer is shown the information in the Cashier the first time, and they can then re-use it which is highly convenient - they can deposit funds without going to the Cashier, or even logging in.
The trade-off in this approach is that customers receive the exchange rate at the moment when the transactions are confirmed on the network, not when they first send them. The exchange is made at the moment when we receive the funds. Therefore, customers can receive a little more/ a little less. The upside of channels for you is, there is minimal customer support required. E.g. for invoices, if customers send funds to a previously used address, you will have to manually reconcile and communicate with the customer.
One key thing to make sure of: once a channel has been created for a customer (when they've made their first deposit request through the Cashier), it's important that if they go back to the Cashier and initiate another deposit, that you display the same channel details to them and do not create a new channel - this is the best user experience.
As cryptocurrency payments are made over a separate network, when creating a channel, we generate a unique payment address for each cryptocurrency so we can match customers to their payments. When a customer makes a cryptocurrency payment, the transaction is then broadcast to the cryptocurrency network for validation/confirmation.
It means that if you want to give the customer an opportunity to make payments not only in Bitcoin, but also in other cryptocurrencies, then in addition to the BTC channel you will need to create more channels for such customers. Once the channel is created, we start monitoring the unique address of the channel to identify any incoming transactions. When we locate an incoming transaction at the channel address, we create a Channel Payment and process it.