Is there a way to purchase credits without a credit card? Perhaps via Paypal or similar?

There used to be, but for some reason (security I think) its a one time use credit/debit card charge

I won't go into the reasons I removed PayPal, but loosely as I am just not comfortable with their policies - for both myself as the merchant as well as you as the consumer. If you're concerned about security, we use Stripe to process our payments, you can read about their security here: https://stripe.com/help/security - and your credit card information never even touches our server. Your card info is sent securely to their server directly from your browser, which in turn sends a one-time use token that we are able to use to charge your card. Even if I wanted to steal your card info, I couldn't. You can verify this by opening up the debug tools of your browser and inspecting the data that is sent to their and our server. (Stripe should accept both credit and debit cards as well)

No, the problem is the non-existence of a credt/debit card. ;)

In other online games I usually pay my supporterships or smiliar always with paypal. So what could people like me do to purchase credits at MFN?

I have used prepaid credit cards here. Typically you can get those most anywhere.