I have read that somebody had problems with statements of the form:
$config = $_SERVER['DOCUMENT_ROOT'] . '/path_from_doc_root_to_udm_custom_ini/udm-custom.ini';
Therefore I am using the absolute path as follows:
$config = '/absolute_path_to_udm-custom_ini/udm-custom.ini';
I was also trying the relative path as suggested by the
"Exhibition Engine" gallery forum, cf.
$config = 'udm-custom.ini';
None of the above settings seem to work. I am a bit lost here.