Can I add a virtual host for subdomain that is hosted by another server?

I followed How To Set Up Apache Virtual Hosts on Ubuntu 18.04 and it is working for two domains, example1.com and example2.com.

Both of them are hosted in a DigitalOcean droplet.

I have another website on Bluehost and I’d like to host its subdomain on the DO droplet. I created a DNS record newsletter.example3.com and www.newsletter.example3.com with my DigitalOcean IP address.

I created newsletter.example3.com.conf:

<VirtualHost *:80>
        ServerAdmin my.name@gmail.com
        ServerName newsletter.example3.com
        ServerAlias www.newsletter.example3.com
        DocumentRoot /var/www/newsletter.example3.com/public_html

        <Directory /var/www/newsletter.example3.com/public_html>
            Options Indexes FollowSymLinks
            AllowOverride All
            Require all granted
        </Directory>

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        <IfModule mod_dir.c>
            DirectoryIndex index.php index.pl index.cgi index.html index.xhtml index.htm
        </IfModule>
        RewriteEngine on
        RewriteCond %{SERVER_NAME} =www.newsletter.example3.com [OR]
        RewriteCond %{SERVER_NAME} =newsletter.example3.com
        RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

I run sudo a2ensite newsletter.cecilieo.com and restarted apache.

sudo systemctl restart apache2

Problem 1: When I go to newsletter.example3.com, it shows example1.com. Problem 2: When I run certbot, it returns errors:

sudo certbot --apache -d newsletter.cecilieo.com -d www.newsletter.example3.com
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator apache, Installer apache
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for newsletter.example3.com
http-01 challenge for www.newsletter.example3.com
Waiting for verification...
Challenge failed for domain newsletter.example3.com
Challenge failed for domain www.newsletter.example3.com
http-01 challenge for newsletter.example3.com
http-01 challenge for www.newsletter.example3.com
Cleaning up challenges
Some challenges have failed.

IMPORTANT NOTES:
 - The following errors were reported by the server:

   Domain: newsletter.example3.com
   Type:   unauthorized
   Detail: Invalid response from
   https://newsletter.example3.com/.well-known/acme-challenge/uMURe80sprzaxrEGzyu7F1CycxEhc-Bd-DVFAM_f09g
   [2606:4700:3030::6815:2eca]: "<!DOCTYPE HTML PUBLIC \"-//IETF//DTD
   HTML 2.0//EN\">\n<html><head>\n<title>404 Not
   Found</title>\n</head><body>\n<h1>Not Found</h1>\n<p"

   To fix these errors, please make sure that your domain name was
   entered correctly and the DNS A/AAAA record(s) for that domain
   contain(s) the right IP address.
 - The following errors were reported by the server:

   Domain: www.newsletter.example3.com
   Type:   tls
   Detail: Fetching
   https://www.newsletter.example3.com/.well-known/acme-challenge/PbVou0UruJkHOZqWPhAOiUWTOkTw6_aMPi-6ScVxyNQ:
   remote error: tls: handshake failure

   To fix these errors, please make sure that your domain name was
   entered correctly and the DNS A/AAAA record(s) for that domain
   contain(s) the right IP address. Additionally, please check that
   you have an up-to-date TLS configuration that allows the server to
   communicate with the Certbot client.

Can I add a subdomain hosted by another server?