Remember that "the accounting formula" is:
Assets = Liability + Equity
Since this entity is More in debt than reflected on the books, you Increase the Loan account (credit) and the Debit is Equity as Retained Earnings or Owner Equity or Unrestricted Net Assets or whatever is your "closing equity" account name.
Putting the amount as an Opening Balance just allows your entry to be lazy and not use the Real Equity; it creates an entry in Opening Balance Equity, which you have to Offset, later. OBE should be 0 and never used again, once a file is set up and in use. There really is no reason to enter it, and then Fix it, afterwards. Just make the right entry, yourself, to start with.