Fortinet Sandbox API Login Request Error

curl -X POST \
https://1.2.3.4.5/jsonrpc \
-H 'Accept: application/json' \
-H 'cache-control: no-cache' \
-k \
-H 'content-type: application/json' \
-H 'postman-token: 593987-1324' \
-d '{
"method": "exec",
"params": [{
"url": "/sys/login/user/",
"data": [{
"user":"username",
"passwd":"PASS"
}]
}],
"session":"1111111111111",
"id": 1,
"ver": "2.0"
}'

if [[ $? -eq 0 ]]; then
echo "API call successful. Response:"
else
echo "API call failed."

fi

I keep receiving an Invalid Request Response "code" 10 in the API response. Does anyone have any suggestions? Some of the other API requests such as the session request work fine so it leads me to believe there is some issue with the given parameters in the request. Any help would be greatly appreciated. Thank you.