Uniswap swap always reverts on Sepolia: UniversalRouter address used with SwapRouter ABI — use SwapRouter02 without deadline

Symptom: an ethers.js script calling exactInputSingle against Uniswap on Sepolia reverts every time, with no useful revert reason. The code imports the ABI from @uniswap/v3-periphery/artifacts/.../SwapRouter.json and sends to an address copied from a UniversalRouter deployment list.

Root cause: the ABI and the address belong to different contracts. Encoding an exactInputSingle call and sending it to UniversalRouter means the selector matches nothing there, so execution reverts. UniversalRouter has an entirely different interface (execute(commands, inputs, deadline) with byte-encoded commands).

Fix: use SwapRouter02, which exposes the familiar exactInputSingle and is deployed on Sepolia (the original SwapRouter is not). One signature difference matters: SwapRouter02's ExactInputSingleParams has **no deadline field** — leave it in your params struct and encoding fails or the arguments shift. So the struct is { tokenIn, tokenOut, fee, recipient, amountIn, amountOutMinimum, sqrtPriceLimitX96 }.

Also verify the token addresses per network: on Sepolia, WETH9 is 0xfFf9976782d46CC05630D1f6eBAb18b2324d6B14. Mainnet addresses copy-pasted into a testnet script are a second, independent cause of unexplained reverts, since calls to an address with no code just fail.

Checklist when a router call reverts with no data: confirm the address hosts the contract whose ABI you encoded (check getCode and the deployments page for that exact chain id), confirm the params struct matches that router version, and confirm token approvals exist for the router you are actually calling. Deployment addresses change — re-read the current Uniswap deployments page rather than trusting an old snippet.

Source: adapted from a Stack Exchange answer by SYED ASAD KAZMI (question by duyanhhz), https://ethereum.stackexchange.com/questions/162588/transaction-got-reverted-uniswap-universal-router — CC BY-SA 4.0