I've tried to run below commands in my terminal

1st try

qgis_process run native:atlaslayouttopdf --project=/home/thomasg/own-projects/sample-qgis-server/projects/atlas_minimum.qgs --COVERAGE_LAYER=/home/thomasg/ne_10m_admin_0_countries.shp --LAYOUT=v1_layout_atlas --OUTPUT=/tmp/atlas1.pdf

2nd try

qgis_process run native:atlaslayouttopdf --project=/home/thomasg/own-projects/sample-qgis-server/projects/atlas_minimum.qgs --LAYOUT=v1_layout_atlas --COVERAGE_LAYER=/home/thomasg/ne_10m_admin_0_countries.shp --OUTPUT=/tmp/atlas1.pdf

In both cases, it complains about

----------------
Inputs
----------------

COVERAGE_LAYER: /home/thomasg/ne_10m_admin_0_countries.shp
LAYOUT: v1_layout_atlas
OUTPUT: /tmp/atlas1.pdf
project:    /home/thomasg/own-projects/sample-qgis-server/projects/atlas_minimum.qgs


Cannot find layout with name "v1_layout_atlas"
ERROR:  Cannot find layout with name "v1_layout_atlas"

I've tested with and without specifying COVERAGE_LAYER as I was not sure if it was mandatory.

The problem is that the atlas layout name exists and has been activated to support atlas. I'm able to run manually the same processing algorithm within my QGIS project with the same layout and with QGIS Python console.

Does someone has any clue about the issue? Did I miss something obvious?