I'm trying to send a transaction to my Nano S but it says the amount is invalid?
The Ripple network doesn't allow an address to have less than 20 XRP. So the first time you'll send a transaction to your device you must send 20 XRP minimum.
I'm trying to send a transaction from an exchange to my Nano S but it says "invalid address"
Some exchanges (such as Bitrex) cannot send transactions on an empty address (the address must be already "activated", which means it must have already a minimum of 20 XRP).
The solution is to ask a friend to send you first 20 XRP, or to withdraw from Poloniex which doesn't have this limitation.
Some or all my transactions are not showing
Simultaneously press Ctrl+Shift+A to reset the transaction history. After cleaning, the next synchronization will recover all your transactions.