Try opening the entry window that makes the most sense for what you're trying to enter (if you're paying a bill for something your company bought, then 'pay invoices' would make sense...), and make the entry.  Before posting it, look at the underlying journal entry.  Unfortunately, I don't use the online version of Sage enough to know exactly how to do this... in the desktop version, it is control-J for journal entry.  If everything is set up properly, you will see that the total amount you are paying to your supplier is showing up as a debit to the #2200 linked account.

This is what the linked accounts for accounts receivable / accounts payable / employee vacation pay payable / employee advances receivable are supposed to do.  They are summary accounts LINKED to all of the underlying details.  #1200 is linked to all of your accounts receivable items - invoices to individual customers, receipts from individual customers, etc.  You should never have to make a general journal entry into this type of linked account, because then your summary account wouldn't equal the total of all of your details!