File Type upload error

Latest update will add webp, but for jfif you need a snippet like so:

<?php
/**
 * Allow .jfif image uploads (it's just JPEG with a different extension).
 * Layer 1+2 satisfy WordPress core; layer 3 satisfies the Events Manager frontend uploader.
 */

// 1. Tell WordPress core .jfif is an allowed type, mapped to JPEG.
add_filter( 'upload_mimes', function ( $mimes ) {
	$mimes['jfif'] = 'image/jpeg';
	return $mimes;
} );

// 2. WP's real-mime check returns image/jpeg for a .jfif file but doesn't know the
//    extension; nudge it through so media_handle_upload() / wp_handle_upload() accept it.
add_filter( 'wp_check_filetype_and_ext', function ( $data, $file, $filename, $mimes ) {
	if ( empty( $data['ext'] ) && empty( $data['type'] ) ) {
		$check = wp_check_filetype( $filename, $mimes );
		if ( 'jfif' === strtolower( (string) $check['ext'] ) ) {
			$data['ext']  = 'jfif';
			$data['type'] = 'image/jpeg';
		}
	}
	return $data;
}, 10, 4 );

// 3. Register jfif in Events Manager's frontend uploader registry (JPEG content).
add_action( 'em_uploads_uploader_init', function () {
	\EM\Uploads\Uploader::$supported_file_types['jfif'] = array(
		'exif_type' => 2,                  // IMAGETYPE_JPEG — .jfif is JPEG data
		'mime'      => array( 'image/jpeg' ),
		'type'      => 'image',
	);
} );

In both cases, in Events Manager > Settings > the uploads/file-types setting, make sure jfif/ webp is in the allowed extensions list (or leave it on “Any Type”).