Leo Wallet stores cryptocurrency called "credits" in separate containers known as UTXOs (Unspent Transaction Outputs) or records. To send credits to someone, you need to use at least two UTXOs: one to cover the amount you wish to send and another to pay a small transaction fee.
Currently, there is a limitation with how transactions are managed. If you receive a single UTXO containing 10 credits, you will not be able to send any of those credits because you need a second UTXO to cover the transaction fee. However, if you receive two separate UTXOs, each containing 5 credits, you can send 5 credits using one UTXO and pay the fee using the other.
The transaction fee is minimal, only 0.025 credits. When you pay the fee, any leftover amount from the fee UTXO is returned to your wallet as change.
The Aleo team is aware of this limitation and is actively working on a solution to make the process more user-friendly. In the meantime, if you encounter this problem, try to ensure that you have at least two separate UTXOs in your wallet to successfully create a transaction.