The error message with code itgenjra007 indicates that the user has NO accessible sites as indicated by a subsequent API call to https://api.atlassian.com/oauth/token/accessible-resources.
Please check that the JIRA user used has been granted access to authorized sites and products for exactly one site. Typically the JIRA OAuth flow lets you choose the site desired.
When verified access rights, please try again to register the JIRA database.