Permission to operate (PTO): the last step before you switch solar on
Written approval from your utility that your system may connect to the grid. It comes after the city inspection, and you must not switch on before it.
After installation and a passed inspection, your installer sends the paperwork to your utility. The utility checks it, sometimes replaces your meter with one that measures power in both directions, and issues permission to operate.
PTO usually takes one to four weeks, longer in busy territories. Switching on before PTO can breach your interconnection agreement and, under net metering, exports before PTO may not be credited.
What this means for you: Put the PTO date in your contract timeline and ask the installer who chases the utility if it stalls.