They need to be a lot more transparent, in many regards really, but also specifically on fees. Your fee could have been due to:
  1. your previous debt to muun (yes they have debt and debt consolidation events)
  2. actual LN fees
  3. what muun charges you in fees
  4. the 2 on chain transactions required for every payment or receive
Muun has been exploited before with 0 conf double spends and I don't think the fee here came from any of that. But they do need to increase the on chain fees or the two 0 conf tx's would fall out of the mempool and never get mined, making it way easier to double spend.
The reason why the fee is so high is because due to high mempool demand, normal transaction fees are about $0.5 It's as simple as that.
As I mentioned further in the thread, I've tested this over and over again on a wallet that has had plenty of funds in it for well over a week, plenty of time for any confirmations. All non-trivial Lightning payments with Muun charge a mining fee, because under the hood an actual transaction has to be made. For trivial payments if low enough value ($1) they appear to just operate on trust.
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Yup, not sure what it's at now, but with low mempools that limit was around 20k sats. If you make a number of payments under that value, it's all trust. Then when you finally hit a big enough payment or go over 20k, you pay the fee for all the previous ones. You could use their recovery tool to get those funds back on chain before it gets to that point. There's several areas where Muun literally lies about your balance in the app too.
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