Propane blockage, how do I fix it?

Disconnect all regulators that are rated for propane use. That may mean crawling underneath and capping all branch lines to appliances. I tend to blow back from the tank location through the supply pipe and towards the open end.

I use 125 PSI air, which my portable compressor delivers. If you notice no detritus exiting the pipe near the removed quick coupler, the fault may be in the coupler, itself. Many are not built well and, if brass, are often made overseas.