[Libguestfs] providing key for luks commands

I am working on building an automated pipeline with a disk that contains a LUKS partition.  since it is running automated i need a method to provide the LUKS key using a file but i keep getting prompted to enter the keys.  I am creating a file with only the key stored in it and using the --key option but i still get the key prompt. here is the command that i am running, can you advise me on what i need to change?: sudo guestfish -a disk.qcow2 --key /dev/sda2:file:key.txt run : part-init /dev/sda msdos : part-add /dev/sda p 2048 500000 : part-add /dev/sda p 500001 2097118 : mkfs ext4 /dev/sda1 : luks-format /dev/sda2 0 : luks-open /dev/sda2 sda2_crypt : mkfs ext4 /dev/mapper/sda2_crypt  thanks​