The error occurs because Odoo expects the journal entry for the invoice to include only one outstanding payments/receipts account, but it seems to have conflicting accounts. Here's how to resolve it:

1. Check the Journal Entry: Go to the Accounting > Journal Entries and find the journal entry linked to the invoice. Look at the accounts used in the entries and ensure there’s only one "Outstanding Payments/Receipts" account (typically an account like "Receivables" or "Payables").
2. Modify the Journal Entry: If there are multiple payment/receipt accounts, you may need to adjust the journal entry manually. Delete any conflicting lines and ensure there's only one payment/receipt account.
3. Reconcile Payments: If the invoice was paid, ensure that the payment is reconciled properly. Odoo might be having trouble because the payment and invoice are not correctly reconciled.
4. Reset the Invoice: Once the journal entry is corrected, try resetting the invoice to draft again.

If the problem persists, it may be worth checking for any customizations or modules that could be causing conflicts in the payment process.