The two most common reasons that a transaction might fail is due to underlying orders being taken before you or the underlying order being cancelled before you confirm.
If the specific bet offer you placed a bet on was taken before your transaction is confirmed, the underlying bet will not execute and you'll be shown an error.
Alternatively, if the specific order you took was cancelled before your bet was confirmed, then the bet will not execute and you'll be shown an error.
What can I do to improve my chances of success?
If you're using MetaMask, be quick in approving the transaction in your wallet. For a betting experience that doesn't require additional in-wallet approval, sign up with email or google and use a fortmatic wallet.
Make sure you are on the latest version of SX Bet by doing a "hard refresh"
Mac OS: Hold down ⌘ Cmd and ⇧ Shift and then press R.
PC: Hold down Ctrl, Shift and the 'R' key or Hold down Ctrl and press F5