When I turn the ignition key, I hear click, click, click and the lights on the dashboard flutter.
Battery is good, lights work well, horn loud so WHAT’s The problem?
Did someone load test the battery and determine it’s OK, or are you basing your “Battery is good” statement on the fact that the horn and lights work?
You’ve described the classic symptoms of a near-dead battery. The horn and lights can work fine and the battery still might not have enough amperage to turn the engine.
I suggest having the battery and the charging system tested. Many auto parts stores will do this free.
Don’t assume battery is good based on horn and lights. Check battery out. Then the starter.
As usual, I agree 100% with McP. Know that it takes only a tiny amount of battery power to operate the dash lights, but a whole bunch to crank the motor over. You likely have enough power to do the first but not the second. Heck, a penlight probably puts out more light than your dashboard.