This is a quick guide that will help you fix the xinput1_4.dll is missing error in Back 4 Blood.
Back 4 Blood xinout1_4.dll Fix
- Go to Computer > Hard drive (Drive C or D) > Windows > System32
- In System32 press control + F, which opens a search bar.
- In the search bar type, xinput1_3.dll.
- Copy xinput1_3.dll and paste it to your desktop.
- Rename xinput1_3.dll for xinput1_4.dll and paste it back to System32
The last thing you have to do is re-open Back 4 Blood and see if the issue has been fixed.