I get a lot of 404s on several of my wordpress posts. All the 404 links have [GPT_URL] at the end.

Examples:

• www.example.com/post-1/[GPT-URL]
• www.example.com/post-2/[GPT-URL]
• www.example.com/post-3/[GPT-URL]

Without the string [GPT_URL] at the end all my links are valid. Not sure what is adding this string at the end. Any suggestions on how I could troubleshoot this?