Hello there, 
don't know is there any french here, so sorry for my bad english.
1 month ago i bought a blackview bv6800pro, and i wanted to install a custom rom like lineage os on it. After a succesful root, i made a mistake w/ TWRP and format totally my phone. 
So i tried to flash stock firmware with SP Flash Tool, but this was unsuccessful. (error DA HASH MISMATCH) and it finished by totally hard brick my phone ( i think it's totally formated, so it can't even boot anymore)
I tried all solutions possible (different versions of flash tools, different roms, etc) but always this error.
Then i found on this forum a tutorial with SP MDT. But again sends me error like scan fail ! then COM ports numbers too repetitive, etc... i dit anything to try to fix this (clean COM ports, uninstall/reinstall drivers, disable driver signature enforcement..) 
Now this has been 1 month i got this phone, and i'm disapointed to loose it, and like the garanty is now void, i don't want to pay to restore it.
That's why i need your best help to find a solution for this ! 
I can send u screens on demand
thanks to all who will read my message!