Is the Lightning network address the equivalent of a static QR code for invoice ?
Yes. Hopefully soon we will get static QR codes for Lightning as well with Bolt12. Right now there are static addresses and one time invoices.
What relates to the QR code that sometimes appears in some websites where people can donate ? Is that the Lightning address ?
The QR codes we have in Lightning now are for one time use of invoices. You can play lnbingoapp.com to try it out, it's pretty cool.
LNURL lets you generate reusable invoices though, can try this with LNBits - highly recommend!
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