Hello Vanessa, 

The issue arises with manually specifying the accounts on the record when you have not specified the Fiscal localization package. Once specifying the package related country preconfigured data like chart of accounts and related taxes will be fetched. Then while creating the contact, the error may not persist.  

Also, find attached the documentation related to fiscal localisation for your further reference:https://www.odoo.com/documentation/16.0/applications/finance/fiscal_localizations.html

Hope this help,
Thank you!

Hi,
You can install a chart of accounts for the company to solve the issue. Or using set defaults option you can set up the default values for this fields:  How To Set Default Value For A Field in Odoo

Thanks