Unable to update the EAH-A1000 firmware.

Make sure your smartphone is connected to the Internet.
Open the Technics Audio Connect app and go to SETTINGS → Headphone information to check the current firmware version.
Make sure the headphones have at least 40% battery charge before starting the update.
Do not turn off the headphones while the firmware is being transferred or installed.
Do not make calls or play music while the firmware update is in progress.
If the firmware transfer remains stuck, force-close the Technics Audio Connect app and then reopen it.