Thank you! That did the trick.
I checked the Apache error log but, at least the log Hostgator provides, shows nothing.
Also, another thing I had to do is move my project directory to the public_html folder. Then, I created the subdomain again and pointed it to that directory.
I’m still very ignorant about how .htaccess works. What’s the difference between
RewriteRule ^ services.php [QSA,L]
and
RewriteRule . services.php [QSA,L]
Thank you so much.