You are using the same certificate for topsnoep.nl and www.topsnoep.nl - for this to work you need to specify both names when requesting the certificate:
It’s probably best to do both, as in my example. That will give you a single new certificate that will cover both names.
You can do the www version separately, but that will give you a separate certificate for it. That’s not necessarily a problem but it does push you one certificate closer to the rate limit, which is something to consider if you have lots of subdomains.
I did as you said. It now works… but still not really. It looks like when I call the https site now it somehow redirects to http. At least I don’t see a lock appearing.
It appears that at the moment the site encrypts only some pages and sends others back to http. However, I am hesitant to send all to https as long as it doesn’t work correctly.
That’s caused by mixed content, some of your images are loaded with plain HTTP. In addition the search form submits to a HTTP page which is also treated as an error by Chrome (Firefox warns only when the form is submitted).
Someone mentioned https://www.whynopadlock.com/, which is a seemingly handy checking tool to diagnose these mixed content (and sometimes cert chain and other) issues. I might start suggesting it to people who have trouble getting the padlock to appear after installing their certs.