Developer registration loop: final submit bounces back to phone verification (SMS accepted)

I cannot complete Meta for Developers registration. The wizard fails silently at the last step and loops back to phone verification, across multiple days, browsers, and attempts.

Steps: open the app-creation page logged in; wizard opens (Register / Verify account / Contact info / About you); SMS code to my +886 number arrives and is accepted; I fill Contact info, pick Developer, click Complete registration; the wizard silently returns to Verify account. No error shown, no developer account created, no Create App option on the Apps page.

Notes: reproduced 2026-09-01 and 09-02, normal and incognito Chrome, extensions off. The phone is already on my Facebook profile in Accounts Center. Some days the SMS is never delivered at all (looks rate-limited after 2 sends/day); when it arrives and is accepted, the final submit still loops.

Goal: create an app with the Threads API use case (threads_basic + threads_keyword_search). What is blocking registration on this account and how can it be resolved?