Infusion cannot be entered. What's going on here? Thank you, everyone.

Before infusion, let the liquid out, let the liquid squeeze out all the air in the infusion tube, and ensure the whole infusion tube to be unobstructed. If the needle is inserted, the infusion can't get in, but it may just be inserted under the skin and not into the vein, so it needs to be pulled out and reinserted into the vein. If the infusion can't get in suddenly in the normal process, it is the blood returning from the infusion tube and the needle is blocked by coagulation. You can squeeze the infusion tube to pressurize the blood in the needle.