Why is there not enough liquidity for an Instant withdrawal?

Instant withdrawal is a feature available in the Tonstakers MiniApp and Tonstakers App. It uses GRAM that is currently idle in the pool and not yet sent to validators. If the available liquidity is insufficient to cover your request, Tonstakers will process it after the current validation cycle ends. You can check the available liquidity on the Unstake page and track the status of your request in your Tonstakers account.