I also had this problem. mount vendor in twrp then unmount it then again mount vendor. then try flashing once again. this is how it worked for me.
---------- Post added at 07:54 AM ---------- Previous post was at 07:45 AM ----------
how do I wipe vendor there is no option in twrp only data storage cache dalvik but when backup and restore there is option for vendor. is it because I didn't wipe vendor I get encryption error on boot. how fix the encryption problem.
Bro, you should use some rec which support vendor.
If not, you can't flash this ROM.