Whenever I try to flash TWRP I get
Custom binary blocked by FRP Lock.
I'm trying to flash with Heimdall.
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On recent Android devices, when you have Factory Reset Protection, which is enabled automatically when you setup a Google account, custom binaries (the files that are not signed by the OEM) are blocked (custom recoveries, boot, etc) for security reasons as one can bypass that lock and gain access to your data.
So disabling OEM lock in the Developer Settings, which opens the bootloader to non-signed binaries, should let you flash any custom binary.
To recover your device, simply flash it with a stock firmware uing Heindall or Odin.