EJabberd and option ldap_tls_cacertfile

Hi everybody.
On my ejabberd we have configured the authentification with LDAPS. All it's allright. But on the LDAPS server , there are now the certificat and certificat autority in SHA256.
Now my connexion is KO.
I try a lot of modification to add the new CA in SHA256 on my ejabberd but it's KO.
I try to insert the ldap_tls_cacertfile parameter in my configuration. with a .pem file. In this file I have the 3 CA (.cer).
But I think my .pem is not OK.
Someone can help me to create a good .pem (format) for the parameter ldap_tls_cacertfile?