What is the minimum XRP Balance?
Ripple enforces a reserve requirement of 20 XRP, which is a minimum amount you need to store in your XRP address in order to protect the shared global ledger from growing excessively large as the result of spam or malicious usage. The 20 XRP is used to activate your address and permit sending and receiving operations.
In order to complete a send transaction on Rain, the receiving XRP address must have a minimum reserved balance of 20 XRP or the sent amount must be at least 20 XRP if the receiving address does not contain the minimum reserved balance of 20 XRP.
If you try to send less than 20 XRP to an address that contains less than the minimum balance of 20 XRP, and if the amount sent to that address is less than 20 XRP, you will be alerted that the balance of the receiving address is low.
If you wish to complete the send transaction you can increase the sent amount in XRP or choose a different address that contains the minimum reserved balance.