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Call exchange(i, j, dx, min_dy) on the pool contract, where i and j are token indices rather than addresses. Verify indices with coins(i) first, quote the output with get_dy(), apply slippage tolerance for min_dy, and approve the pool to spend your input token.

Empty reverts usually mean the ABI does not match the pool type or the wrong index type was used. Older pools like 3pool use int128 for indices while newer factory pools use uint256. Simulate with simulateContract to surface the revert reason before sending.

exchange() swaps between a meta pool's direct coins, while exchange_underlying() swaps between the meta-asset and the individual tokens inside the basepool. Calling exchange() when you need a basepool token like USDC from a LUSD/3CRV pool will revert.

LLAMMA gradually converts collateral to crvUSD as the price moves through your selected bands instead of liquidating instantly at a threshold. If the price recovers, it converts back. Health approaching zero means bands are fully converted, and negative health allows hard liquidation.

USDT requires the current allowance to be zero before setting a new non-zero approval. Check the existing allowance, reset it to 0 with a separate approve(spender, 0) transaction if needed, then set the new amount.

Deposit your LP tokens into the pool's gauge contract, which you can find via the MetaRegistry get_gauge() function. Rewards accrue over time and are claimed by calling mint(gauge_addr) on the Minter contract, not on the gauge itself.