The tank is under the vehicle so its design is such that I don't open valves, though there is an emergency cutoff.
You stated in previous posts that you have opened or closed a valve. In one post you state that you don't know which way to turn it to open it.
I'd suggest to take your problem to an RV service garage or call a mobile technician proficient in propane systems. Ask him to show you how the service valve opens and closes. Mark an arrow on the valve so when you forget which direction to turn, it is clearly marked.