You do not need to diagnose the gate before calling. A clear description of what happened is plenty. If you can, note whether the gate is a swing or sliding style, whether it uses solar or electric power, what the operator does when you press the control, and whether the problem began suddenly or gradually. A photo or short video can also help explain an intermittent issue.
There are a few basic checks that are reasonable for a property owner: make sure no vehicle, branch, rock, or other visible obstruction is in the gate’s path; replace a remote battery if it is clearly weak; and look for a tripped breaker only if you can do so safely. Do not reach into moving parts, disconnect springs or arms, defeat photo eyes, or repeatedly force a gate through a fault. Those shortcuts can turn a repair into a larger problem.
If the gate is stuck open, stuck closed, or behaving unpredictably, keep the area clear and let us know how the issue affects access to the property. If you have the operator manual, keep it nearby for the visit. That lets the service visit start with the right priorities.