If this is a memecoin or shitcoin with tons of supply like trillions or whatever, in order to sell it on PancakeSwap you either need to increase your slippage to make the transaction or check if there is enough liquidity on that pool or tokens you are traded. Chances that there is no liq ( or rug pull imminent) but in some cases the slippage used isnt enough try to increase it lime by 2 points every try and if its work the transaction would be process.