FLsun Q5 pause printing with Gcode

[salmec]

dear Community
I would like to add a pause to the printer automatically by Gcode.
I use Orcaslicer and with this software is possible to insert a pause in a certain layer.
The code added to the Gcode is: M400 U1

But it doesn't works...
I've also tried M600 (used for filament replacement) without success.

How can I pause the print automatically without pressing pause button on display?

Thanks in advance

Salmec