添加到购物车ajax / index / add / uenc错误Magento

So Magento "suddenly" gave me this error:

POST https://www.samplesite.nl/ajax/index/add/uenc/aHR0cHM6Ly93d3cub3ZlcnRyZWt…IyMC5odG1sP19fX1NJRD1VJnN0b3JlPQ,,/product/1383/form_key/f7PMMUeIktiFmSpv/ 404 (Not Found)

I haven't added a plugin or something what-so-ever it just suddenly appeared. So what I understand out of this question is, that the link is incorrect. Unfortunately, I have very little knowledge of Magento. I did not understand how to fix this from that question.
So how do I fix this? Where is the file located? What code needs to be altered to fix this?
Or maybe another solution?

Thanks in advance!

Many possibility possible in this case like

  • New extension installed
  • Already installed extension configuration change
  • Theme setting change
  • Override add to cart url method

so you have to check one by one case in your magento. If you still not find the problem then let me know.