Is this field also defined on you python file ? 

Are you you upgrading the correct module ?

Sharing the log files would also be helpful

Hi,

If you're encountering an internal server error when loading an Odoo 15 XML view, there are a few key areas to check. First, ensure that the is_invoice field you're referencing in the attrs is actually defined and available in the model or view. If this field doesn’t exist, Odoo will fail to render the view. Second, confirm that the fields l10n_id_nik and l10n_id_tax_name are properly defined in the Python model (.py file). If these fields are missing, the view will throw an error at runtime. The syntax of your attrs dictionary looks correct, so that’s likely not the issue. To find the exact cause of the internal server error, check your Odoo logs using the command: tail -f /var/log/odoo/odoo-server.log. 

This will show you the real-time error traceback, which usually points directly to the missing field, incorrect logic, or another issue. Once you address the specific error shown in the logs, your view should load without problems.

Hope it helps.