In order for BigSIS to best help you, especially around troubleshooting issues, we need access to your Authorize.net account. You can create a BigSIS user: https://account.authorize.net/UI/themes/anet/user/AddUser.aspx
The username should be based on the domain of your website Url (usually also your BigSIS installation Url), so if your BigSIS Url is: https://demo.bigsis.com/admin then you should create a user called bigsis.demo (please start with bigsis. and then add your school's website / BigSIS sub-domain).
Ideally you would grant us the permissions in the second image below. This will allow us to be able to fully access, troubleshoot and manage your Authorize.net account in order to best help you with your payment management. These are all permissions that we have via the API, but having UI/Web access is extremely helpful.
We do not need to be able to create more users or update your information, just access to see and change transactions, like our tool does in the API.
If you are not comfortable with any of the permissions we are requesting, let us know and we can discuss. We can work around your needs, but this will be the easiest way for us to assist you.