On page
https://www.wapt.fr/en/doc-1.5/Installation/security/install_ssl_certificate.html
you write:
"Example: echo srvwapt.mydomain.lan.crt ca.crt > cert.pem"
Well, will that not only produce a file called cert.pem with this content:
'srvwapt.mydomain.lan.crt ca.crt'

Should you maybe use "cat" in your example instead of "echo", and also
two >-signs?

Like this
"Example: cat srvwapt.mydomain.lan.crt ca.crt >> cert.pem"