How do the different API Settings work with STC and STCtoCart?

API Settings:

• Manual <-- Default setting, you log into STCtoCart and process orders by manually sending them to STC.
  
  
• Semi-Automatic <-- Only new orders that are in "Processing" status are sent to STC automatically and then updated to "Warehouse" status if order is accepted. As before no email notice is sent to the customer. Zen v1.39b and v1.39c has a new option in the shopping admin for orders to be hidden from customer view. STCtoCart uses this new setting to hide what it does from the customer. 
  
  
• Full Automatic <-- Does what Semi-Automatic, plus checks "Warehouse" status to see if it's been shipped and if so updates the shopping cart to "Shipped" status. If Zen 3rd party module "Ty Package Tracker" installed then adds tracking number. As before no email notice is sent to the customer.

You should do everything in Manual mode until you are sure all is working correctly. You'll also want to make sure you have a credit card on file with STC so they can charge your order. Even being setup as a qualified buyer and with a credit card on file it's possible that something at STC may trigger this response: 

This is not an error with STCtoCart, it's the response that STC is sending back. You'll want to contact STC to find out what the problem may be with your account.