So I have the following Rewrite Rules:
RewriteRule ^([a-z0-9_\\-]+)(\\.php)?$ index.php?page=$1 [NC,L,QSA] RewriteRule ^([a-zA-Z0-9_-]+)/$ index.php?shop=$1&
In your second rule, add ? after trailing slash:
?
RewriteRule ^([a-zA-Z0-9_-]+)/?$ index.php?shop=$1&page=index [NC,L,QSA]
That will make trailing / optional
/