The files required for flashing (boot.img dtbo.img vbmeta.img) via fastboot can be found in the file payload.bin, which is to be extracted from the file e-1.15-t-20230918331436-dev-troika.zip.
Now flashing additional partitions first
fastboot flash vbmeta vbmeta.img
fastboot flash dtbo dtbo.img
The e-recovery file is called boot.img
fastboot flash boot boot.img
Now reboot into recovery to verify the installation.
Now tap Factory Reset , then Format data / factory reset
Return to the e-recovery main menu
adb sideload e-1.15-t-20230918331436-dev-troika.zip
That’s all. Happy flashing!