Cannot flash twrp-3.2.3-0-cedric.img (Motorola Moto G5) ("Image not signed or corrupt")

I have followed all the steps of this guy but flashing twrp-3.2.3-0-cedric.img failed. When I open my Ubuntu console and type fastboot flash recovery /home/username/folder/twrp-3.2.3-0-cedric.img, it says: (bootloader) slot-count: not found (bootloader) slot-suffixes: not found (bootloader) slot-suffixes: not found (bootloader) has-slot:recovery: not found target reported max download size of 536870912 bytes sending 'recovery' (14572 KB)... OKAY [ 0.463s] writing 'recovery'... (bootloader) Image not signed or corrupt OKAY [ 0.502s] finished. total time: 0.965s What did I do wrong? Did I use the wrong version? Looking at this similar problem did not help me. sudo fastboot flash recovery /home/username/folder/twrp-3.2.3-0-cedric.img does not help either.