Individual enrollment fails with "unknown error" (HTTP 406, resultCode 202018)

Hi, I'm trying to enroll in the Apple Developer Program as an individual. After selecting "Individual / Sole Proprietor" and accepting the license agreement, the page shows "We are unable to process your request. An unknown error occurred."

The request behind it, POST /services-enrollment/submitIndividualEnrollment, returns HTTP 406 with resultCode 202018 ("Your request could not be processed").

What I've checked:

• The enrollment eligibility check shows an existing individual enrollment in draft status, stuck at the billing info step
• Two-factor authentication is on, and I've added a US phone number to match my account's US region
• I've retried several times, with the same result
• I've contacted Developer Support and am waiting for a reply

Questions:

1. What does resultCode 202018 mean?
2. How can I finish or reset a draft enrollment that's stuck at the billing step?
3. Will enrolling as an organization (I'm requesting a D-U-N-S number now) conflict with the stuck individual draft?

Thanks for any help!