Hi,
The Epson WF-3540 was listed as a supported printer in a July 01, 2022 About AirPrint article, but it is not mentioned in the latest March 13, 2024 edition. The printer could have an old AirPrint/firmware version. You may want to check whether the firmware can be updated.
About AirPrint - Apple Support
Use AirPrint to print from your iPhone or iPad - Apple Support
Please double-check all settings. A Wi-Fi network password change would be made on the router.
See also the following tip by Lawrence Finch.
AirPrint Troubleshooting - Apple Community
If nothing else helps, you could perhaps try the Epson iPrint app, which seems to support the WF-3540.
https://apps.apple.com/us/app/epson-iprint/id326876192?platform=ipad
https://support.epson.net/appinfo/iprint/en/