Nginx: Rewrite rule for subfolder
Solution 1:
You must not escape the period (.) in the second part of the rewrite:
rewrite ^/example3\.com/(.*)$ /example3\.com/index.php?id=$1 last;
should be
rewrite ^/example3\.com/(.*)$ /example3.com/index.php?id=$1 last;
But what does your id look like? If it's a number, you could try this out:
location /example3.com/ {
index index.php;
rewrite "^/example3\.com/([0-9]+)$" /example3.com/index.php?id=$1 break;
}