Why does not send letters and requests from the site?

Question

PHP

On a new VPS under Ubuntu 16.04, I installed Apache, MySQL + PhpMyAdmin, PHP according to the instructions - DigitalOcean .
Then I installed the script. The same script with exactly the same code works successfully on another server, but here, when registering, a letter is not sent to the mail and, most likely, for some reason it does not send a request to Instagram to authorize the account, the script itself gives an error that authorization failed.
Perhaps I missed and did not install some module on the server? In truth, the other day I first encountered installing and configuring web servers and LAMP.
See site .
Help me please.

Answer 1

it is desirable to look at the logs
+ soap by default can be disabled, on DO, most likely, for sure

Answer 2

Go to the mail server logs and look
And in general check that you have installed it

Answer 3

Test from command line: Mail server running?
ps auxf |grep [p]ostfix