Taxed token swap fails: why the route may be incompatible

A fee-on-transfer token deducts value during its own transfer logic. A route that expects every transferred unit to arrive can fail when the receiving contract gets less. This is separate from the aggregator’s displayed service fee.

Check compatibility before tolerance

Uniswap’s v3 developer documentation says its router contracts do not support fee-on-transfer tokens. Other routes can have different support, so verify the actual path instead of assuming all DEXes behave alike.

A higher slippage tolerance cannot fix every accounting assumption. It can permit a worse outcome, including a token deduction, but it cannot make an incompatible router handle that token correctly.

Read the fee conditions

Determine whether deductions apply to buys, sells or ordinary transfers and whether authorized parties can change them. Some behavior depends on the sender or recipient. A quoted percentage may therefore fail to describe the exact route you are about to use.

Uniswap’s expected-failure guidance lists variable token fees as one reason a swap can fail preflight. Treat that warning as a reason to inspect the token rather than automatically accepting a very wide tolerance.

If a supported route exists, compare the actual minimum output after all deductions and network costs. If the token’s rules remain unclear, a small test is not a guarantee for a later larger sale. Preserve the contract and failure evidence; do not confuse a failed sell with a permission problem without checking the transfer rules.