The web service endpoint returned a "HTTP/1.1 403 Forbidden" response There are 12 or so similar questions but not drupal related.
Here is my site on a digitalocean  droplet: http://104.236.27.226/

It is apache2 on ubuntu16 php7. 
I am using: 000-default.conf:

ServerName casey.com
ServerAdmin webmaster@localhost
DocumentRoot /var/www/html
&lt;Directory "/var/www/html"&gt;
  AllowOverride All
  Require all granted 
&lt;/Directory&gt;


I made file permission as permissive as possible:

drwxrwsrwx  4 casey    www-data 4096 Sep 20 12:15 www/


I put an echo in the settings.php, at the very end to show the user for  apache:

casey@dchouse02:/var$ tail -n 3 www/html/sites/default/settings.php
echo('&lt;h4&gt;ECHO: from setting.php after databases array; and apache user is (via exec whoami): '); 
echo exec('whoami'); echo ('&lt;/h4&gt;');


Knowing that settings.php is being read, I moved to indx.php for this D7 site:

casey@dchouse02:/var$ tail -n 3 www/html/index.php 
echo('&lt;p&gt;from index.php: before menu_execute_active_handler:&lt;/p&gt;');
menu_execute_active_handler();
echo('&lt;p&gt;After menu_execute_active_handler&lt;/p&gt;'); 


At this point the error appears:

The web service endpoint returned a "HTTP/1.1 403 Forbidden" response 


The list of apache processes look similar to what I get from the ubuntu on my laptop:

casey@dchouse02:/var$ ps aux | grep apache
root     16068  0.0  4.7 327752 23512 ?        Ss   16:59   0:00 /usr/sbin/apache2 -k start
www-data 16071  0.0 10.2 345548 51244 ?        S    16:59   0:00 /usr/sbin/apache2 -k start
www-data 16072  0.0 10.2 343656 51176 ?        S    16:59   0:01 /usr/sbin/apache2 -k start
www-data 16073  0.0 10.7 347648 53632 ?        S    16:59   0:00 /usr/sbin/apache2 -k start
www-data 16074  0.0 11.1 349660 55520 ?        S    16:59   0:01 /usr/sbin/apache2 -k start
www-data 16075  0.0 10.1 345548 50888 ?        S    16:59   0:01 /usr/sbin/apache2 -k start
www-data 16099  0.0 10.0 343428 50248 ?        S    16:59   0:00 /usr/sbin/apache2 -k start
www-data 16764  0.0 10.3 345600 51792 ?        S    18:37   0:00 /usr/sbin/apache2 -k start
www-data 17344  0.0  1.3 327784  6612 ?        S    21:38   0:00 /usr/sbin/apache2 -k start
www-data 17347  0.0  1.3 327784  6612 ?        S    21:38   0:00 /usr/sbin/apache2 -k start


I don't know what else to do to troubleshoot  this.
This is a pretty basic error most likely having to do with your digital ocean config than Drupal. You've got a named virtual host (casey.com) in your config file. Not sure how pointing us to an IP address helps us to help you.

Read through the digital ocean server set up documentation and make sure you've covered all your bases.