If your secret key contains certain characters (usually that means anything except letters and numbers) it is possible that the server denies to serve the request and throws a 406 error. Do note that it is the web server that blocks the request. At the time the request is blocked Joomla! has not even run yet, so there is none of our code being executed. As a result we can not provide any solution other than to tell you to use a less complex secret word, ideally consisting of at least 14 letters and numbers (but no punctuation or other special characters).
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
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