"Fee too low" Alert/tooltip is very badly needed

[2pac1]

When sending a large payment (2000$ for example) via Thunderhub, onc might forget that nodes that this payment will go over charge in percentage of the volume moved.

So fee of 10 or 100 will not do the trick, and the error will not give any info about what is going on. Fee of 1000 will not do the trick as well as if you are connected to a node that is taking 0.05% of volume moved, then you will need 1748 sats + base fee (probably 1 sat) in order to send 3 496 629 sats. That is a long way from default's settings and one might try 20, 40, 50 and will never come to 2000.

Error popping up saying: your Maximum fees are set too low. Nodes you will be routing charge both base fee + fee based on the volume moved. So the larger the amount being sent the larger the potential fees. To send 3 496 629 sats via node that charges 0.05% of volume moved, you need to set fees to 2000 as they will be slightly lower than that.

Other idea would be some sort of calculator where it could suggest what the fees will be: https://lnrouter.app/get-route > similar to this

Or to add something like this that will be educational as well:

How Are Fees Calculated? Every node in the route charges a certain fee. The fee consists of a constant base fee and an amount dependend fee per volume moved.

Formula: base fee + (fee for 1 sats moved * total sats-being-sent) = fee