VestingBalance

The account's balance is locked under a vesting schedule, leaving too little usable balance to send the requested value. Check the account's Vesting schedules and its lock in Locks, and compare the unvested (still locked) amount against what the transfer needs.

Declared by the Balances pallet; it classifies to the semantic code insufficient_balance.

Remediation

Fund the signing account or reduce the amount; check with btcli wallet balance

The same explanation is available in the terminal: btcli explain VestingBalance.