Hello,
addHeader and addFooter methods only work with a single section. For this reason, the mergeDocx method available in Advanced and Premium licenses is needed to generate documents with multiple sections with different headers and footers (https://www.phpdocx.com/documentation/cookbook/headers-and-footers-for-sections).
If you need to overwrite headers or footers in a DOCX that contains one section, please note you may need to set all scopes (not only the default scope):
$docx->addFooter(array('default' => $numbering, 'first' => $numbering, 'even' => $numbering));
If you need to overwrite headers or footers in a DOCX that contains one or more sections, you can use the importHeadersAndFooters method (importing a DOCX that also includes all scopes of the headers/footers to be added: default, first, even):
$docx->importHeadersAndFooters('docx_footer.docx');
Regards.