There is an issue currently where users aren't able to submit new apps on Developer.PayPal.com. There are a couple potential workarounds that you may want to check.
Ensure that your Developer.PayPal.com account has a first and last name associated with it and that you have a "facilitator" account saved in the "Sandbox accounts" section. If you don't have a "facilitator" account you can add one by just creating a new account with the e-mail address formatted like this - xy-facilitator@domain.com
I'll update this thread again when a fix is released or if more information is provided.
Edit: The issue where valid accounts were unable to submit an application should be fixed now. Make sure that the account you're requesting an app for is on this list and you should be good to go: https://developer.paypal.com/webapps/developer/docs/integration/direct/rest_api_payment_country_currency_support/