By design, Accounts Receivable and Accounts Payable type of accounts having the Eliminate Intercompany Transactions preference checked require Intercompany Customer and Intercompany Vendor name to be associated respectively in a journal. Since there is no option to set in a name when entering an opening balance, you may follow the steps below:
1. Navigate to Setup > Accounting > Enter Opening Balances > populate the following field:
--Set an amount for the intercompany account.
2. Hit Save.
***Result: Elimination settings for the journal line, account, and name do not match. To check this line for intercompany elimination, you must check Eliminate Intercompany Transactions on the account record and enter a To Subsidiary on the name record, if used.
3. Alternatively, you can set an amount for another account and hit Save.
4. Edit the journal entry created from step 3 to set the correct account and populate the following field:
--To subsidiary > you might need to customize the form to expose the To Subsidiary field.
5. Hit Save.