This is a non-LEGO piece since none of the LEGO parts have gaps as seen in second picture.
One thing to note. Actual LEGO elements (depends on the version of Technic, Axle Connector 2 x 3 with Ball Socket) tend to crack right where the gap is on this clone element.
Finally, I did it. I wasted two days waiting for answers when the solution is actually very simple.
I just lifted the box cover with my fingertips just a tiny bit, so that there was enough space to stick something thin between the box cover and the box itself. I did not lift as much as possible because:
My fingers would slip and drop the box lid again, ...