Try it live at electrum43.org
The Electrum bitcoin wallet uses a custom base 43 encoding on data before it is displayed as a QR code. See the "base_encode" function here:
If you used a QR reader to transfer data from electrum off of a machine, you need to be able to transform that into a hex string before bitcoin will know what to do with it. This project offers a webpage and a js library that will decode the Electrum base 43 format.
For example, if the QR code you read was a transaction that you signed on an offline airgapped machine, after using this project to decode it you could use blockchain.info to decode the hex data or broadcast the transaction