@Luthi, Hi Lucci, welcome to the forum. Please read How to get the best out of this forum.
Any suggestion about what it can be ?
Yes, there is something wrong with your wiring. Looks like your SPI communication doesn't work.
I need complete information to be able to help. It is frustrating to have to ask back.
Please post a link to your e-paper panel or board and to the connection module (if separate).
Tell which processor you used, a link if not a common one.
Please report the wiring you used. And the constructor line you selected (old style), or the driver class definition and constructor line (new style).
Also report the example you used. Diagnostic output is preferred in a code window.
Jean-Marc