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Tried cashu to shopstr and the token failed a few times, but eventually gave this message and then worked.
But trying to make a test purchase and it says I don't have a balance even though it's displayed in the wallet section. nostr:npub15dc33fyg3cpd9r58vlqge2hh8dy6hkkrjxkhluv2xpyfreqkmsesesyv6e 
Discussion
nostore extension on safari.
After some investigation, the problem isn't associated with your wallet balance; the returned error message just doesn't reflect all failure cases. The listing you were testing on either:
1) Doesn't have a supported/valid currency,
2) is less than 1 sat,
or
3) the Alby exchange rate API failed to return a value due to latency, network, or timeout issues
Ah ok that makes sense, I'll try a higher balance with a better connection and see if that works.