t-field requires a record.field_name access pattern. open_balance is a Python float (returned by _fp_account_summary_open_balance), not a recordset attribute, so QWeb threw AssertionError at render time and the page 500'd. Format the value in the controller via tools.formatLang and render it as a plain string with t-out instead. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>