• Some or all my transactions are not showing
On a Mac OS computer your need to uninstall and reinstall the Ripple wallet.
On a Windows computer you need to press Ctrl+Shift+A to reset the data.
After cleaning, the next synchronization will recover all your transactions.
• I'm trying to send a transaction to my Ledger Nano S but it says the amount is invalid.
The XRP network does not allow an address to have less than 20 XRP. The first time you send a transaction to your Ledger Ripple wallet 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 Bittrex) 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.