You report that neither the gas grill nor the gas fire pit work. I presume you are using a quick connect
? I also presume neither appliance has its own regulator. This is a low pressure connection controlled by the regulator at the propane tanks. No other regulators allowed.
If so, replace the "female" quick connect. If yours has the lever-control ball valve, the ball valve may be stuck closed - the handle may no longer rotate the ball valve. Hell, the screw holding the lever in place might be loose and just need tightening. Also, there is a primary ball valve that is opened when you insert the male. Perhaps something is plugging up the works.
Before you install the new female quick connect, first verify that there are no sources of ignition (sparks/flames) nearby, then CAREFULLY and with the help of a second person, BRIEFLY open the propane tank valve to determine if gas flows through the line. Crack it open for a moment and then close it.
If there is gas flowing, you'll know immediately because of the smell, and you may also hear it hissing. Let the gas dissipate and install the new female. Before anyone has a brain hemorrhage over this, this act is no different than opening the valve on the fire pit and then using a lighter to ignite the fire. This line is down-stream of the main regulator, so propane will flow at "low pressure" through the line. Why THIS test? It's always possible that a stone or other object flew up and pinched the soft copper line distributing gas to that port. It's HIGHLY unlikely, but this will be a good way to verify continuity of the gas line. If there is little or no flow, trace the gas line back to the intersection where it branches off to feed things that are working. Somewhere in there, you'll find a crimp or other source of blockage. If you don't find a crimp, with the gas off, consider disconnecting the copper line (typically a flare fitting) from the junction where everything else works, removing the quick connect, and using an air compressor to blow out the line. I can't imagine what would block the gas line, but perhaps there is debris in the line from assembly, and that debris clogged your old quick connect. If there is a rubber pigtail joining the copper line to the quick connect, remove it from the copper and examine that hose for blockage or other issues.
That last paragraph includes lots of speculation, but your description narrows the problem to that one branch of the propane distribution circuit. There aren't many options. And propane is not known to block up 1/4" or larger copper tubing.
If you have flow, and you have a new female quick connect on the line, and if things still do not work....maybe you have a bizarre coincidence...a double failure of your appliances. Utterly bizarre for sure, but possible.
First DOUBLE CHECK your new female quick connect. Use the new male that came with it (nothing attached), plug it into the female, then do the same gas flow test described above. With the quick connection made and the ball valve open, have your partner briefly open the propane tank valve. If you have gas flow, you have two "bad" appliances.
Most likely culprit? The orifice on the output of each flame control valve (no regulators on these "low pressure" devices right?) The orifices might be plugged for some reason. Take them off the flame control valves, grab 'em with vice grips (they are tiny) and hit them with about 40 PSI or more of air pressure. I cleaned a gas grill orifice once, and the crud that came out was shocking! Since these low pressure devices have only a male quick connect (probably unprotected) on the end of a hose, anything could get in the line, including spiders (just like your hot water heater burner tube), dirt, kool-aid, or chocolate pudding. The flame control valves might be gummed up, too. Let's hope it doesn't come to this.