Please add a functionality where when generating an invoice you can enter the amount in any Fiat currency rather than in Satoshi.

Currently you cannot know in real time how much that amount of satoshi equates to. We have to use an external tool for such things.

In a PoS scenario how the person handling the tab will know the amount of satoshi to enter in the app and show to customers ? He would have to use an external tool.

If possible add this feature show an option to enter in a default pre configured Fiat currency, but also allow people to choose another one if necessary.