To use this app you need to sign up for an account with Sendle. Shipping costs will be charged by Sendle and will vary based on the size/weight, source/destination of the packages sent, and your account plan.
Sendle shipping rates can be found here: https://try.sendle.com/pricing
How do I sign up for a Sendle account?
To sign up for a Sendle account, please visit: https://www.sendle.com/users/sign\_up