spams not prevented with captcha

I'm using quip comment for Articles. I've used random text captcha on quip comment form but it is still not preventing spam links. Any other suggestions to stop spam links to be inserted on quip comment box ?

Try using the math option.

In some parts of the world where wages are very low, they hire people to manually submit spam, which makes it pretty difficult to block them.

Thanks BobRay. How can I use math captcha on quip comment form?

I haven't used it, but I did find this: https://forums.modx.com/thread/76629/quip---add-simple-anti-spam-field