If it helps, here’s my experience: I added my phone number and pretty much implemented every trick you guys suggested on this thread and it didn’t work. I contacted Twitter, told them about this thread and how many were having issues due to the phone number, and over the weekend, they were able to get back to me with the following email
Hello,
We’re aware of an issue that occurs for users who have added a phone number immediately prior to attempting to create a new key. While we work to resolve, you should be able to create a new key after waiting 5-10 minutes. Please reply to this ticket if you continue to experience the error and we will respond as soon as possible.
Regards,
Twitter Platform Operations
And now I can create an app and in fact just did. I’m really impressed sith Twitter customer service (many other firms don’t even bother to get back to you) and hope that the issue is resolved for others as well. If not, try waiting a day or two.