[One (M8) Q&A, Help & Troubleshooting] speedee39:
I received an unlocked HTC One M8 (US, works on AT&T, not Harmon Kardon), factory reset, never been modded. Because it ran Android 6.x, I was concerned that it wasn't as secure as it could be, so I researched how to install the newest Android possible. I found many articles on these forums, guides from 2014 all the way to 2016. I didn't (and still don't) know enough to tell the difference between a good tutorial and a bad/outdated one. I saw that some tutorials were edited to reflect new mods, but now that I have read even more, I suspect that even those updated ones are now obsolete.

My problem is that I installed Resurrection Remix with v7.1.2, along with pico Open Gapps, and it won't let me install several apps like Chrome or even YouTube. I have decided that I don't want a newer ROM and I would rather just revert to stock. I have been attempting to revert to stock for the last three or four days, and I have spent many hours researching and reading (mostly this site...go figure), but so far I have not accomplished anything.

Current information about the phone: I did not make a backup (I've had little success doing this over the years on Android phones), I unlocked the bootloader with the HTC unlock code.bin file, the phone has S-ON and has not been rooted. In fact, I've tried SuperSU and Sunshine and neither worked. I have TWRP 2.7.1.0 installed. I have drivers from HTC Sync, but I also installed the Android Studio, along with some utilities that come with it. I have attempted the RUU from HTC (RUU_M8_UL_M60_SENSE70_MR_BrightstarUS_WWE_6.12.1540.4) and it always says that there was an error.

I have attempted several times to change the CID, but only because a tutorial told me to. I assume that it was changed when I installed the Remix mod. I have no idea what it should be. I have attempted to install firmware as well, both with the adb method and by copying it to the SD card and renaming it for bootloader, but both options fail. The adb method fails with...

(bootloader) zip info parsing...

FAILED (remote: 99 unknown fail)

...and the SD card method thinks for a bit, then says "press power to reboot" in the same type of text as the bootloader text.

I am only a little familiar with adb and fastboot, so please, be gentle. If you list commands, I will use them without even thinking, like how Ron Burgandy reads everything on the teleprompter.

Please help.

Here's the getvar:

(bootloader) version: 0.5

(bootloader) version-bootloader: 3.19.0.0000

(bootloader) version-baseband: INVALID_VER_INFO

(bootloader) version-cpld: None

(bootloader) version-microp: None

(bootloader) version-main:

(bootloader) version-misc: PVT SHIP S-ON

(bootloader) serialno: XXXXXXXXXXXX

(bootloader) imei: XXXXXXXXXXXXX

(bootloader) imei2: Not Support

(bootloader) meid: 00000000000000

(bootloader) product: m8_ul_ca

(bootloader) platform: hTCBmsm8974

(bootloader) modelid: 0P6B17000

(bootloader) cidnum: GOOGL001

(bootloader) battery-status: good

(bootloader) battery-voltage: 0mV

(bootloader) partition-layout: Generic

(bootloader) security: on

(bootloader) build-mode: SHIP

(bootloader) boot-mode: FASTBOOT

(bootloader) commitno-bootloader: 11459804

(bootloader) hbootpreupdate: 11

(bootloader) gencheckpt: 0