In addition to the creditor/debtor level, it is possible to set a standard journal for purchase invoices and sales invoices at the accounting record settings.
Go to the cogwheel and click on ‘Accounting records’. Click on the magnifying glass behind the relevant administration and click on ‘Settings’.
Here you can set the default journal for purchase invoices (purchase journal) and for sales invoices (sales journal)
The standard journal is always used, unless the debtor/creditor indicates on which journal the invoices must be posted. In that case, the setting at the creditor/debtor level will be used.