In /plugins/extensions-for-two-factor/includes/class-two-factor-extensions-sms.php (the Two_Factor_Extensions_SMS class), there’s an issue in the generate_and_send_token() function where if you’re using the WP SMS plugin, the wp_sms_send() function’s first parameter needs an array of cell numbers, not a string.

The plugin current sends that function a string, and it is later filtered out by wp_sms.

inside the generate_and_send_token() function, change:

} elseif ( function_exists( 'wp_sms_send' ) ) { // WP SMS plugin.
			return wp_sms_send( $to, $message );
		} else {

TO:

} elseif ( function_exists( 'wp_sms_send' ) ) { // WP SMS plugin.
			return wp_sms_send( array($to), $message );
		} else {

This will fix the issue.