SMS verification code never arrives - Meta for Developers signup

I'm trying to create a Meta for Developers account to integrate the Messenger Platform for my business (Facebook Page). I'm stuck at the "Verify account" step - the SMS code never arrives, even after clicking "Resend SMS" multiple times.

What I've tried so far, all unsuccessful:

• 3 different Vietnamese mobile numbers, across 2 different carriers (Vinaphone and Viettel)
• - Using "Update mobile number" to switch numbers directly in the verification dialog
• - Retrying in Incognito mode (Chrome desktop)
• - Retrying from a mobile browser (Chrome on Android)
• - Successfully completed phone verification via Accounts Centre > Two-factor authentication (SMS arrived fine there) before retrying - the Developer registration flow still didn't skip the "Verify account" step and still failed to send a new code

Since the Accounts Centre SMS verification worked normally, this seems isolated to the Meta for Developers registration flow specifically, not a general carrier/SMS delivery issue on my end.

Could someone from Meta look into why SMS verification codes aren't being sent for this specific flow, or manually verify my account so I can proceed to create an App?