wildanimal

And it is not only issue with WP Mail SMTP, we used few mail modules before it, which based on Google API Library — there is same exact issue with them as well.

• This reply was modified 6 years, 5 months ago by wildanimal.

Hello Oguz,

It depends in which sequence WordPress loads both modules. If WP Mail SMTP loaded first – you will get fatal error in log file when your frontend user will click Confirm and Submit Appointment (it send ajax request to proceed appointment which gives 500 server error).

I spent time yesterday to debug it and found that it happening just because WP Gmail SMTP has own version of Google API Library (v2.2.1) and it is not full library there, it contain only files related to Gmail API. As Google_Client is essential part for Google API Library and both extension has own version of it when Appointments+ plugin trying to work with Google_Client loaded by WP Mail SMTP plugin it crashes, as some of functions was deprecated in Google API v2.2.1 comparing to v1.1.5 which uses by Appointments+.

You can see that in beginning of /wp-content/plugins/appointments/includes/external/google/Client.php file, there is condition:

if (!class_exists(‘Google_Client’)) {
require_once dirname(__FILE__) . ‘/autoload.php’;
}

which does not allow to load own version of Google API Library v1.1.5, because WP Mail SMTP loaded it before, so it is already exists and as a result Appointments trying to operate with wrong version of Google API Library (v.2.2.1).

Exact error happening in class Appointments_Google_Calendar_API_Manager:
$this->client->setLogger( new Appointments_Google_Calendar_Logger( $this->client ) );

It inherited Google_Logger_Abstract where in __construct function it calling:
$client->getClassConfig(‘Google_Logger_Abstract’, ‘level’)

But Google_Client v2.2.1 does not have getClassConfig function anymore. It has getClassConfig in v1.1.5 but not in v2.2.1

I hope I gave as much as possible details to describe case in details. And yes, it have been working 1 week and then by no reasons it fail again – it happened 3 times in a row (during 3 weeks), so we just didn’t understood what cause the issue until yesterday when I spent full day to find this problem.

Also I found on WP Mail SMTP support forum that people mentioned same issue with Appointments plugin.

Exact name of the plugin name which we use to integrate with Gmail API is WP Mail SMTP. https://www.ads-software.com/plugins/wp-mail-smtp