Support got back to me very quickly! The fix is as follows:
/**
* Allow PDFs in ACF Gallery fields (ACF 6.8.7+).
*
* ACF 6.8.7 added server-side enforcement that restricts Image and Gallery
* fields to image files only. These three filters restore PDF support while
* leaving the image-only restriction in place for every other file type.
*
* To target a single gallery field instead of all gallery fields, replace
* /type=gallery with /key=field_XXXXXXXX in all three filter tags.
*/
add_filter( ‘acf/get_image_mime_types/type=gallery’, function( $mimes ) {
return $mimes + array( ‘mp4’ => ‘video/mp4’ );
} );
add_filter( ‘acf/validate_is_image_attachment/type=gallery’, function( $errors, $file, $attachment ) {
$type = ! empty( $attachment[‘id’] )
? get_post_mime_type( $attachment[‘id’] )
: ( wp_check_filetype( $attachment[‘name’] ?? ” )[‘type’] ?? ( $attachment[‘mime’] ?? $attachment[‘type’] ?? ” ) );
if ( ‘video/mp4’ === $type ) {
unset( $errors[‘invalid_image’] );
}
return $errors;
}, 10, 3 );
add_filter( ‘acf/validate_value/type=gallery’, function( $valid, $value, $field, $input ) {
if ( true === $valid || ! is_array( $value ) ) {
return $valid;
}
foreach ( $value as $id ) {
if ( ! is_numeric( $id ) ) {
return $valid;
}
if ( ! wp_attachment_is_image( $id ) && ‘video/mp4’ !== get_post_mime_type( $id ) ) {
return $valid;
}
}
$min = (int) ( $field[‘min’] ?? 0 );
if ( $min && count( $value ) < $min ) {
return sprintf(
_n( ‘%1$s requires at least %2$s selection’, ‘%1$s requires at least %2$s selections’, $min, ‘acf’ ),
$field[‘label’],
$min
);
}
return true;
}, 20, 4 );
