QuickBooks Online (QBO) is not designed to work with multiple Accounts Receivable (AR) and Accounts Payable (AP) accounts.  The initial AR and AP accounts, or those selected during conversion, will be the default accounts. QBO encourages their customers to merge their accounts payable and receivable accounts into one.

In QuickBooks Online (QBO), the default Accounts Payable (AP) and Accounts Receivable (AR) accounts are selected during the initial account setup. Those are the accounts Bill.com transactions will sync to where applicable. 

• If there are multiple AP and/or AR accounts in QBO and Bill.com, transactions will still always sync to those initially set default accounts, unless they are deleted or merged in QBO.
• If the initially set default accounts are deleted in QBO, Bill.com will sync to the remaining active oldest AP and/or AR accounts, as those become the new default accounts in QBO.
• QBO will not allow users to delete the default AP and/or AR accounts without a replacement account having been created first, as that new account will become the new default in QBO.
• QBO will also not allow users to delete the default AP and/or AR accounts in QBO if there are any transactions in the register. If the default AP and/or AR accounts need to be changed in QBO, and the existing default AP and/or AR accounts have transactions in the register, the new default AP and/or AR account(s) must be created first, then merged with the original default AP and/or AR accounts. The resulting accounts become the new default AP and/or AR accounts, to which Bill.com will sync transactions.
• If the old inactive default AP and/or AR accounts are reactivated in QBO, they are not restored as the defaults; whichever accounts were set as the new defaults as per the processes above will stay in place as the defaults unless those specific accounts are deleted or merged.

Please see the QuickBooks Online article Can I change the default A/R or A/P account in QuickBooks Online? for more information.