PHP zip file downloads locally but not in production - php

Question

I am working on some files to download in a zip. Works fine locally but not in any environment (staging or production). Using WP VIP also, not sure if that helps. I'm a little new to VIP. Really racked by brains here and can't seem to figure out the issue.
I've read the resources on PHP zip creation. I do get the "Unable to add zip file.', 500 );" error producing.
Code below:
$context = [];
$post = theme()->twig()->create_post();
$tab_index = filter_input( INPUT_GET, 'tab-index', FILTER_SANITIZE_NUMBER_INT );
$content_calendar = $post->get_field('content_calendar');
if ( ! isset( $content_calendar[ $tab_index ] ) ) {
\wp_send_json_error( 'Invalid tab-index.', 400 );
exit;
}
$tab = $content_calendar[ $tab_index ];
// Create zip name;
$name = 'content-calendar-' . $tab_index;
$group_index = filter_input( INPUT_GET, 'group-index', FILTER_SANITIZE_NUMBER_INT );
if ( null !== $group_index ) {
if ( ! isset( $tab['groups'][ $group_index ] ) ) {
\wp_send_json_error( 'Invalid group-index.', 400 );
exit;
}
$groups = [ $tab['groups'][ $group_index ] ];
// Append group to name
$name .= '-' . $group_index;
} else {
$groups = $tab['groups'];
}
// Extract paths from resources with assets
$paths = [];
foreach ( $groups as $group ) {
foreach ( $group['resources'] as $resource ) {
if ( $resource['social_resource'] ) {
$asset_id = get_field( 'asset', $resource['social_resource'] );
if ( $asset_id ) {
$paths[] = get_attached_file( $asset_id, true );
}
}
}
}
// Remove invalid or duplicate URLs
$paths = array_unique( array_filter( $paths ) );
if ( empty( $paths ) ) {
\wp_send_json_error( 'No files to download.', 400 );
exit;
}
// Generate file names
$zipfile = wp_upload_dir()['basedir'] . '/' . $name . '.zip';
$zipname = $name . '-' . date('Y-m-d') . '.zip';
// Generate file
$zip = new ZipArchive;
if ( true !== $zip->open( $zipfile, ZipArchive::CREATE | ZipArchive::OVERWRITE ) ) {
\wp_send_json_error( 'Unable to create zip file.', 500 );
exit;
}
foreach ( $paths as $path ) {
if ( true !== $zip->addFile( $path, basename( $path ) ) ) {
$zip->close();
\wp_send_json_error( 'Unable to add file to zip.', 500 );
exit;
}
}
$zip->close();
// Send headers and stream file
header( 'Content-Type: application/zip' );
header( 'Content-disposition: attachment; filename=' . $zipname );
header( 'Content-Length: ' . filesize( $zipfile ) );
readfile( $zipfile );
exit;
Any help is appreciated.