Connection of a video intercom

Thank you for your response.
What I bought is not a video intercom, but an intercom and, at the time (6-7 years ago), video intercoms were not as widespread and mandatory (Disability Law on intercoms and access control).
Moreover, when buying a complete kit, do we really think about measuring the provided flush-mounted box just in case we decide later to upgrade the equipment to a different model from the same brand?
No, I’m sorry, but we should expect that the equipment supplied by the same manufacturer fits into all the mounting boxes from said manufacturer.
In electrical work, all standard sockets and switches fit into mounting boxes, and this has been the case for many years. Sometimes you have to juggle with clips for boxes that are not equipped with fixing screws, but that’s all.
I have often managed to install recent electrical equipment on boxes that are over 30 years old...
While one can understand, by adopting a competitive logic, without condoning it, that telephone or video intercom boxes do not have dimensional standards so that one cannot install a device from another brand in place of a specific brand, it is more complicated to understand the incompatibility between devices from the same brand.
And this is true for both older and newer models!
Finally, at Extel, almost every recent model does not fit without "hacking" into the boxes of another model.