Since you don't say what make and model of toilet or how old it is we can only guess what is causing your problem. It may be construction debris in the line or if yours has a screen in the valve it could be plugged. Or the foot pedal may need adjustment. It could be a sign that someone didn't bypass the water heater when draining the plumbing through the low point drains and sucked water heater sediment into the rest of the plumbing.
Richard & Jill
2014 Flagstaff 832IKBS Classic Super Lite
2018 Silverado 1500 Crew Cab Z71 4WD All Star Edition
Camping since 1989, seasonal since 2000
Car Shredder Op/Tech, Scrap Metal Recycling - retired
I deserve hazard pay when camping with my relatives.