The usual method for entering accounts receivable opening balance is to simply enter one transaction for each outstanding invoice.
The other way to post the opening balance is to import it as an AR transaction, which in the end has the same result as entering it manually.
Decide which method to use by determining if creating a spreadsheet with the correct layout will be more or less work than manually entering them. The spreadsheet layout is critical and the import will fail if it is not correct.
Opening Balance entries should include at least the following, which is the minimum required to make sure that the data is aged properly.
- Invoice Number
- Date
- Amount
The date cannot be before that first fiscal period available for posting. Usually when starting new company data, that date is at least one year prior. If the date of the invoice is older than that, just use the earliest date possible so that the aging will be at the maximum value from Company Settings / Accounts Receivable / Aging periods.
Optionally it should also include:
- PO number
- Terms
- Memo