Hi, Accounts payable and receivable are most likely are link control accounts at the moment hence you will not able to find them under general journal

You can only post in them if you un-link them.  Or  you can get a hold of an Accountant's version which allows you to post to link accounts

You should able to find them in  Setup, Settings, Customer and sales/Vendor and purchase (A/R or  A/P), Link accounts.

Please be careful if you are using foreign currency and have foreign invoice outstanding, because if you un-link it , it will reset the foreign value to home value.

(I would recommend you check the Maintenance, Data Integrity summary, see if you will cause data inconsistency, because by updating A/R or A/P through general journal, it increase left side value on the summary only)

More details in the Knowledge base article 10399

31/12/14 Accounts Receivable XYZ Inc - Account No. 1205  - Debit - 7592.20
31/12/14 Accounts Payable                    - Account No. 2100  - Credit - 7592.20

you know the customer 'xyz inc', I presume they are also a vendor (the entry refers to both AP/AR)
I also presume you owe this customer 7592.20 (ar credit) and
              they owe you the same amount (ap debit)

so using a clearing a bank,
  create a one-line invoice for the customer for this amount
    no tax
    account = clearing bank

    this will
      db ar
      cr clearing bank

  receive payment, and apply the existing credit to this invoice

  create a one-line purchase invoice for the vendor for this amount
    no tax
    account = clearing bank

    this will
      db clearing bank
      cr ap

  pay purchase invoice, and apply the existing credit to this invoice

  and the clearing bank balance has a net change of 0.00