If you want to work with the Eve Swagger API (ESI) then your account needs to meet certain criteria. This is for a few reasons, one of which I imagine is to prevent people from making bogus third-party dev accounts to make disruptive applications.
Regarding the requirements to register an application for the use of ESI I believe your account needs to have a verified email address and a paid subscription (at least at some point). If you don’t meet these for some reason and you are unable to do so, file a support ticket at https://support.eveonline.com . They should be able to put you in touch with the right people to see if there is something you are missing or something you can do. Alternatively, you could join the #tweetfleet dev slack channel and talk to people and some of the API devs there as well.
On a side note, just a friendly reminder for anyone thinking of developing applications to work with Eve’s API system use ESI; as XML and CREST will be turned off in a few months.