Try using the 'faucet-mainnet' command with your Ethereum wallet address to receive MATIC for transaction fees.

To transfer USDCoins from your Ethereum wallet using the Polygon network, you'll need MATIC to pay for network fees.

For additional guidance or technical assistance, you can explore Polygon's tools, such as the Polygon Portal, which provides asset management and gas refueling features .

If you are still unable to proceed, consider checking if Moonpay's services are currently operational as reported by other users, confirming through official support channels if necessary.