`/Order/{order_guid}/true<BLOCKED>`

I am getting these errors in my elmah logs in an angular js .net mvc application.
I tried to google about but there is not much information about what it means.
All I found was people trying to remove this error from their application by turning off validation.

In my case this is a production application open to public and I want to make sure that it is secure.

I meant to ask cyber security experts out there, is it something concerning? What advise would you give to secure my application from such attacks.