Hello Erik Vojtas,

For set default value in fiscal_position_id may be below code will helpful for you.
First create the record in data file for account.fiscal.position after that give the xml_ID into the default function

def _get_default_fiscal_position_id(self):
return self.env.ref('XML_ID', raise_if_not_found=False).id

fiscal_position_id = fields.Many2one('account.fiscal.position', string='Fiscal Position', default=_get_default_fiscal_position_id)





Module: sale.order: How to set default value for fiscal_position_id
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