A required template option is missing.
Some output plugins require specific template options. The template bound the the action is question does not contain this option and thus is rejected.
The most prominent example of required template options is the "SQL" set of options that many database output plugins require. This is done because if neither of these options is present, a sql injection (security issue) would happen. As such, most database plugins require one of these options (note that it is possible to write database plugins that work without this option in a secure way, it is depending on the approach taken by the plugin developer).
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