Your developer account application was not approved. You may continue to manage existing apps, however, further action may be taken if they violate [Twitter policies]
All of our developer applications are reviewed to ensure compliance with Twitter policy. While we can’t comment on specific cases, applications may be rejected if they are found to be in violation of any section of the Developer Agreement and Policy, Automation Rules, Display Requirements, and/or the Twitter Rules.
Additional information on restricted uses of Twitter APIs is available here.
There currently isn’t a way to edit a rejected application, or to re-apply, however stay informed for product updates/changes.
There are several existing topics on the matter. I’m going to close this one as it is a duplicate.