adb sideload factory mode file ends up in error

On Pixel 8a, I was trying to downgrade from Android 15 to Android 14. So, I downloaded https://dl.google.com/dl/android/aosp/akita-ap2a.240905.003.a1-factory-39b3cda7.zip which is the last factory release of Android 14. However, adb sideload the above zip ends up in an error. It says: ERROR: recovery: footer is wrong ERROR: recovery: Signature verification faield ERROR: recovery: error 21 Install from ADB completed with status 2. Installation aborted. On the top of the phone, I also get WARNING: Previous installation has failed. Your device may fail to boot if you reboot or power off now. And Reboot to bootloader is highlighted. Should I be doing this? The other options are Reboot system now (unlikely this should be done given the above message) Enter fastboot Apply update from adb Apply update from sdcard Wipe data/factory reset Mount /system View recovery logs Run graphics test Run locale test Power off What should I be doing here? Would wipe data/factory reset resolve the issue? I may note that I checked the sha256sum and it does match. I can try sideloading again, but the device is no longer listed at this point.