Hello, I have this issue of having a 403 error everytime I try and access my app on my FB Canvas page. What could be the issue? I haven't changed the links of my site. Let me know thanks! I have attached a file to show.
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That error is from the built-in Firewall of Akeeba's Admin Tools. Please try disabling that and see if the issue goes away. If so, check the log of AdminTools to determine why the content is being blocked.