Problem 

The create button only returns a warn message with the following text: "Cant create the issue. The configured Jira responded the following .." 

Solution

One or more required Fields are not included in the "Issue Form - create form" or hidden (and there is no default value specified)

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Problem

The create button only returns a warn message with the following text: "Anonymous access must use CAPTCHA."

Solution

Since version 2.3, non logged in users of Confluence can create Jira Issues. But these users have to fill in a captcha.

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