OpenSSL error: 1416F086:SSL routines:tls_process_server_certificate

Hi all,
I have a problem when I'm trying to send mails - Marketing -> Mail.
I'm using OpenCart 3.0.2.0.
These are my settings:
Mail Engine: SMTP
SMTP Hostname: tls://smtp.gmail.com
SMTP Username: myusername
SMTP Password: mypassword
SMTP Port: 587

The error is:
Warning: stream_socket_enable_crypto(): SSL operation failed with code1. OpenSSL Error messages: error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed in C:\xampp\htdocs\opencart\system\library\mail\smtp.php on line 140

Anyone has an idea how to solve the problem?
I'm new in OpenCart (we use it at the university, so my experience is not so much).

Thanks in advance.

I heard around the forum recently that Gmail is no longer accessible via remote websites. Better to configure your emails with a reliable provider to resolve this issue.