After reading through this, it seems to me the crux ofnthe problem is that the error itself is unknown so wallets cannot provide more details and remain truthful.

The UX side of this issue is users don't understand. They don't necessarily need more accurate info on what went wrong, but rather simply thay something did go wrong and what miiiiight be some likely culprits. Most users dont care what went wrong technically and its not the wallets job to educate but nudge the user in a direction so they can ask for help knowlegably.

I propose a message such as:

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Unknown Error. Payment failed and was not routed.

Potential reasons:

Paying an invoice that is already paid.

Payment cannot reach destination. No viable routes.

[Help link with possible culprits so user can knowlegably ask for help]

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