The Truth
The "Unlock OEM" feature in the developer settings
is only used to restore the stock update regardless of FRP being enabled or any type of actual "Google" interference of the restore. The setting does not actually unlock the bootloader. Yes, You could use CROM and it will say it's successful however it will not be for non-Chinese devices. The bootloader is still locked and this is
why you are getting secure check fail. I know what you are thinking at this point...what about fastboot? Sorry, This is one of those Samsung devices that does not fastboot.
THE OEM UNLOCK FEATURE DOES -NOT-UNLOCK THE BOOTLOADER! Do not think that if you enable the oem unlock, that it will magically allow you to install TWRP.
CROM does not unlock it either. CROM will report that the bootloader is unlocked however it will not be.
The TWRP located on the TWRP Builder website is is for an older version of the firmware for the phone. You cannot downgrade the stock firmware once you updated it. That means you cannot install the May 2018 update if you have the July 2018 update installed. The TWRP build could be updated to match the latest recovery build however that is completely pointless and a waste of time at this point
until you can actually find a way to actually get the TWRP installed. If you want TWRP on a device that has a bootloader, you might actually have to gain root beforehand and install TWRP with the TWRP installer. There is some "special" cases where you actually can install an engineering firmware or a very very early test firmware then you can root that, install TWRP, and then upgrade android (modifying the latest firmware version so that it doesn't update the recovery and keeps TWRP) so that you can have TWRP on the latest build. This was a method used on one of the Verizon variants of the Galaxy S5.
Well since you guys have all the heartbreaking news, here is the kind of good...
Tracfone is not very responsible when it comes to making sure their phones are up to date and even are sloppy (You might have noticed the duplicated stock ringtones, haha). This means that it could be possible for someone to find an exploit in the latest firmware or one of the internals (engineering firmware) then gain root access. The only issue you can actually run into here is -getting someone knowledgeable to take the job-. I've recently obtained a 727vl and can guarantee that with root, this phone might actually be worth something rather than a cheap android.
I'll put this here for additional information just to show that it is possible for a locked bootloader:
https://forum.xda-developers.com/ve...oot-method-t3561529/post71202995#post71202995