A deposit increases your account value, but it may not increase your available balance. Legend uses cross margin by default, so a new deposit becomes shared collateral for your open positions.

Your available balance can stay at $0 when:

Your open positions have unrealized losses.
Margin is reserved for open positions or open orders.

What to do

Look at your account value, not only your available balance. The deposit is included there.
Close a position, reduce a position, or cancel open orders to free margin.
Deposit more funds.

Read Account equity, available balance, and margin for the full explanation.