There are several reasons why a transaction can fail when using Uniswap:
Transaction deadline expired
The Uniswap interface sets a transaction deadline of 20 minutes to prevent users from swapping after significant price movement. Your transaction may reach the 20 minute deadline if your network fee limit is set too low.
You can try to initiate the transaction again, or adjust your network fee settings to a higher price.
The Uniswap interface sets a default slippage limit of 0.5%. This slippage limit is the different between your expected output and the real output at the time of your swap. If the real output changes by more than your set slippage, the transaction will fail.
At your own risk, you can adjust the slippage limits in ‘Transaction settings.’
If you do not have enough of your network’s native token to cover the network fees, you will not be able to execute a transaction. Each transaction requires this network fee to execute a transaction.
You can purchase more of your networks native token, adjust your swap amount, or wait for network fees to drop.
Token not supported by Uniswap
Deflationary tokens are not supported by the Uniswap v3 router. If you are try to execute a transaction with any of these tokens, the transaction with automatically fail. Here is a list of deflationary tokens that are not supported.