my propane generator won't start

Make sure the Propane Regulator is adjusted for proper gas pressure. The generator uses lots of propane. If the furnace, stove, and/or water heater are running, the generator may be "starved" for fuel if the gas pressure is too low. You may also need to replace the standard propane regulator with a "high-flow" model.

https://www.championpowerequipment.com/wp-content/uploads/2021/09/201122-EPL-English-all.pdf

I see an air filter and a fuel strainer. Since the strainer is attached to the fuel tank you aren't using; I'm guessing it's the air filter, or the repair service never fixed it at all.

I never tried running on gasoline, because I did not want to contaminate it. I wanted this generator to run only on propane. I used to have a gasoline generator but I had to  get it serviced each year. I wanted to avoid that, so I purchased this propane generator. When I mentioned "intake filter", that's what I thought the repair guy said, but he might have meant something else. I just remember the word filter, not exactly what kind.

But it runs on gasoline?

Gonna need more info. LP inline filters are cheap and easy to replace. And many are cleanable 

It could be just me but I’m not sure what you are referring to when you say “intake filter”. Do you mean the filter on the gas line or the air filter.