OnePlus 10 Pro - can't unlock bootloader as serial # is only 7 digits

Recently bought a T-Mobile OnePlus 10 pro from eBay that is carrier but not bootloader unlocked. I got it specifically to root since it's a T-Mobile variant which can be unlocked using an automated process.

But when I tried to unlock the bootloader I discovered the serial number on the phone is 7 digits and the system will only accept 8.

I sent an email to support several days ago but have not gotten a response and the OnePlus subreddit deleted my post. I'm hoping maybe someone here has had or heard of a similar problem and could maybe suggest a solution?