First, you must link the apaleo's hotels/properties to an odoo's company. You can do that in the menu "odooConfig". You see all your apaleo's property in the list. In the column "Company" you can select the appropriate odoo's company. You can link more apaleo's properties to one odoo's company, or you can do 1:1 mapping.
For the defined apaleo property and odoo's company, you have to define/select the journal for the transaction import. The list in this field provides or journals with the type "Miscellaneous". You can see all journals in your odd application in accounting in menu Configuration->Journals and you can define there a new journal for the apaleo transactions.