Hello everyone,
I have a leveling problem with my Floureon J1 3D printer.
I don't know if it can be useful to identify the model,
on the user manual the one highlighted in green I think refers to my printer:

Before the first print I started the automatic leveling using the sensor supplied and then I manually set the Z axis.

I did both operations using the printer firmware directly from the cursor, following the instructions on the LCD as follows:

I performed this tutorial step by step, which the company sent me


Once the automatic leveling procedure was completed, in which the printer performed different measurements on the entire plate,
I tried to launch the first print but the nozzle remains about 3mm away from the plate even if in the "home" position the distance from the plate would seem correct.

How can I fix this? What am I doing wrong? It seems that the leveling is not successful and I do not understand how to solve

thank you very much in advance