TWRP Backup and Recovery on TX3 Mini

I am having problems trying to get a full backup using TWRP for this box.

I have followed instructions on another thread but with no success.

Here's what I have done:-

Copied S905-TWRP3-VIT.zip to the root directory of my micro SD card

Installed TWRP manager and used to get box into reboot recovery

Selected apply update from EXT

Selected update from SD card

Selected the zip file

Now the first error message I get is footer is wrong and the recovery fails

Could someone explain what I am doing wrong please?

Thanks