cat >bl.wl << EOF
and
the
of
in
on
at
a
an
to
that
is
EOF

curl -c cookie.txt \
    -i \
    -F "username=<username>" \
    -F "password=<password>" \
    "https://the.sketchengine.co.uk/login/" > /dev/null

curl -b cookie.txt \
    -i \
    -X POST \
    -F "corpname=bnc2_tt21" \
    -F "wlsort=f" \
    -F "wlattr=word" \
    -F "format=json" \
    -H "Content-Type: multipart/form-data" \
    -F "wlblacklist=@bl.wl" \
    "https://the.sketchengine.co.uk/corpus/wordlist" > result.json

cat result.json