The "cashuB" format is a new token format that is not get supported on the site (yet). You should be able to toggle the tokens to "legacy" in order to get a "cashuA" token, if I am not mistaken.
Discussion
Only on some wallets. I also found that on android brave and chrome browsers using amber, many of the interactions fail since they open a new tab on each amber request and the main shopstr site never gets the clipboard signed data. This makes it useless. I've only had the site work successfully from desktop using nos2x extension. But still glitchy. I suppose I can use a new sec and add it directly and use that personality for shopstr to test further and see if built in nsec works better.
Relay connection and performance issues have been reported when using chromium-based browsers; will be one of the next focuses to make the site more data efficient.
As for the Amber sign-in, yes, unfortunately that's the expertience for Android signers with websites, but we will also be adding bunker support soon, which is another way of using Amber.