Example of how to send files to the remote server.

remote-post-with-files.php

	$boundary = str_repeat( '-', 24 ) . wp_generate_password( 16 );
	$headers  = array(
		'content-type' => 'multipart/form-data; boundary=' . $boundary,
	);

	if ( ! isset( $files['path'] ) ) {
		$error_message = 'Invalid arguments';

		return array( $success, $error_message, $word_count, $individual_word_count );
	}

	$body = '';
	foreach ( $files['path'] as $index => $file_path ) {
		$body .= '--' . $boundary . "\r\n";
		if ( 0 === $index ) {
			$name = 'file';
		} else {
			$name = $index - 1;
		}
		$body .= 'Content-Disposition: form-data; name="' . $name . '"; filename="' . basename( $file_path ) . '"' . "\r\n";
		$body .= 'Content-Type: ' . $files['type'][ $index ] . "\r\n\r\n";
		// phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
		$body .= file_get_contents( $file_path ) . "\r\n";
	}
	$body .= '--' . $boundary . '--' . "\r\n";

	$max_execution_time = 600;
	set_time_limit( $max_execution_time );
	$timeout = ini_get( 'max_execution_time' ) - 5;
	$timeout = $timeout < $max_execution_time - 5 ? $max_execution_time - 5 : $timeout;

	$remote_args = array(
		'method'      => 'POST',
		'headers'     => $headers,
		'redirection' => 0,
		'body'        => $body,
		'timeout'     => $timeout,
	);

	$word_count_ip_address = fq_get_option( 'word_count_ip_address' );

	$result = wp_remote_post( 'http://' . $word_count_ip_address . '/a/uploadMultiple', $remote_args );