The password that you use to connect OnTrac with Shippo is not that same as what you use to log in to their website. You'll need to get what's called an API password from them.
Since this is private and sensitive information, there's no way for us to get this for you - you will have to email SoftwareSupport@ontrac.com or call them at 877-225-6837. You should provide them with your account number so they can issue you an API password. If you have any trouble, please contact us.