execute doctl using cronjob + shell script failed

i have this following code to make droplets (and another shell script code to destroy this droplets), I want to cron this code on the cronjob but failed, can anyone tell me how to cron doctl?

#!/bin/bash
#set environtment variable
database_id=$(<./config/database_ID)
region=sgp1
num_nodes=3
size=db-s-2vcpu-4gb

#create readonly
echo "create readonly on ${database_id}"
for i in {1..10}
do
        echo "create db-ro-${i}"
        doctl database replica create $database_id db-ro-$i --size db-s-4vcpu-8gb --region $region
done

#resizing database
doctl databases resize $database_id --num-nodes $num_nodes --size $size  -v