To take a payment, you need 3 components.
- An Online form/App - This is Payments2Us (Payments2Us also includes receipting, deduplication, events, memberships etc).
- A Payment Gateway. This connects the form with the card holders bank - no matter where they are on the planet and transfers the funds to the Merchant Facility.
- A Merchant Facility. This is like a line of credit. If the card holder queries the transaction, the funds go back to the card holder form the merchant facility.
The Merchant Facility then puts the funds into your bank.
For item 2, your organisation has selected Authorize.net.
For item 3, this can be with Authorize.net or any other provider of Merchant Services.
You will also see in the error message ""The Global Payment System Identification numbers are incorrect. Call Merchant Service Provider." that says to contact the "Merchant Service Provider" - This is what is described in item 3 above.
You will see when signing up for Authorize.net that they have the option of item 2 only OR item 2+3 - https://www.authorize.net/en-us/sign-up/pricing.html
So, you need to contact Authorize.net and ask them to add/setup a Merchant Facility. Or, ask them for guidance on how you get this setup.