Zou dit eventueel een oplossing zijn?
Ik weet niet of spotweb op een andere directory staat.
If your spotweb installation is not in your www-root dir, but in a subfolder, you should add a line with the RewriteBase in your .htaccess.. It should look like the following (change the third line for your situation):
RewriteEngine on
RewriteCond %{REQUEST_URI} !api/
RewriteBase /spotweb/
RewriteRule api/?$ index.php?page=newznabapi [QSA]
RewriteRule details/([^/]+) index.php?page=getspot&messageid=$1 [L]