btrfs error creating fs with LUKS

hi, 
i've been following this tutorial (tried few others in past, but found this the best)... just learning the steps needed to encrypt my drives. and have been advised to encrypt my drives using btrfs. as only want/need to use with linux... afaics, it's the best option for me. for encrypting large drives 1-2TB (will use for 32gb usb too). 

so, here's the link to website i've used (but also referred to few others, none clearing up query):

https://www.linuxfordevices.com/tutorials/linux/encrypting-partitions-with-luks

this is the command causing issue:

sudo mkfs.exfat /dev/mapper/map_point -n volume_name

(i've changed it to suit me, to:
sudo mkfs.btrfs /dev/mapper/31gb_Tosh_1 -n toshiba)

tried few variations, even without the flag. 

will attach screenshot with error msg. 

i expect the flag is wrong. or i need to change the command to suit btrfs. 

any tips appreciated. thanks. 
phil

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