[LG V20 Guides, News, & Discussion] soroner:
If you panicked, ran step3.bat and bricked your phone like I have (had), un-brick your phone and restore it to stock with Prowler_gr's amazing LGUP force flash solution.

https://xdaforums.com/v20/how-to/guide-patch-lgup-to-unlock-features-t3652222

"KDZ file is invalid" is gone!!!!! Restore your phone to its great musical potential!

I tried everything to restore my phone before finding this, flashing the four .img files from dirtysanta (don't do this) and buying new USB cables etc. (I thought the haunting screen glitch after the several bricked fails of my phone was calling out to me), so my phone was on another level of brickedness. But this works! My LG V20 returned to me from audio heaven. I was ecstatic.

Download mode (Hold the down volume button, then insert usb cable to a PC with ADB/Fastboot installed) is obviously needed. You'd probably need to drop your V20 from outer space or added some random files from the chaotic void for download mode to not be enterable. Yes, you need a PC with ADB/Fastboot (and LG mobile driver obviously, but how would you brick your phone without even the basic necessity?) installed. Go borrow the library PC if you have to.

Steps to unbrick your LG V20 for those who didn't follow instructions exactly like me the first time:

1 -

You need to download the .kdz file of your (yes, and I mean YOUR) phone's model, exactly to the letters printed at the back of the battery compartment or box (so H990N is NOT H990, OR H990DS, it's H990N, don't flunk this, the file is like 2.5 GB) from https://lg-firmwares.com - Look for a file that have been uploaded before 2017.

2 -

By this point you probably either a. don't have the correct LGUP_Common.dll file (you're supposed to extract it using WindowsLGFirmwareExtract from the downloaded .kdz file) or b. the file you have no longer works. If either is the case, LGUP won't start or would pretend that your phone doesn't exist. Prowler_gr's files come with a LGUP_Common.dll file. Place it at <directory where LGUP is installed> /LGUP/model/common (if theres no file named common, make it).

3 -

Now is the revelatory part. Assuming that you have LGUP installed by now, get Prowler_gr's phonesaving, patched LGUP file and put it into the LGUP folder. Replace the original. This is the savior that will no longer look down on you for rooting your phone poorly and incorrectly. Plug your V20 in download mode to your PC and fire up the patched LGUP file, and prepare to save your great music phone.

Now, follow the instructions - carefully and deliberately - at https://xdaforums.com/v20/how-to/guide-patch-lgup-to-unlock-features-t3652222 (pay attention to the screenshots). I successfully recovered my H990N LG V20 with this. This saved my phone from a thorough brick, the screen was over 17 layers of static, but now its actually EVEN FASTER than before thanks to the amazing power of root (not to mention the developers - can't resist, praisee - leicxan and jahlex - for an incredible kernel that automatically disables the root checker and thus the lagginess as well as automatically editing the build.prop file to bypass the Android API 48khz audio resampling - saved me from having to troubleshoot 4 different kernel crashes with the RTCD root checker app and to use the no-search function ES file explorer app to edit the files every reboot!)

My LG V20 is much faster, much better and much more customizable after I've successfully rooted it (and I always have a reliable backup with Prowler_gr's patched LGUP!) With Nova Launcher and KLWP, I have my own customized (much nicer visually than stock) user interface that's not going to be found in any smartphone ever. Being one of the remaining flagships with a removable battery (i.e. you don't need to replace your phone every 2 years AND you don't need to quick charge to make that lifespan even shorter with a simple battery replacement!), an IR blaster, very useful notification secondary display not found in other smartphones, most sophisticated manual camera/video modes of smartphones AND the 32 bit Sabre ES9218 DAC that's newer than the DACs found in ~300 to 1000$ dedicated audio players, the LG V20 is absolutely the best power user phone out there right now, and I'm glad that it has the most free development attention as it rightfully deserves to have!

Everyone here on XDA making our phones beautiful and powerful are awesome!!!