Swap transactions in Xverse on the Stacks network may be optionally sponsored. When a transaction is sponsored, the sender does not have to pay the associated transaction/miner fees. A third-party sponsor will sponsor and pay for the fees. Both the sender and the sponsor will sign the transaction before it can be broadcasted.
To sponsor a swap transactions powered by ALEX, you must not have any pending Stacks transactions on the same wallet address. This is a limit set by ALEX's sponsor service to ensure potential nonce issues do not affect the continued functioning of the sponsor service.
If you would like to make a swap transaction and have a pending transaction, you can choose to wait until the pending transactions have been confirmed before becoming eligible for sponsorship. Alternatively, you can pay for the swap transaction fees from your own wallet without sponsorship.