I entered just my apartment number in that field no "apt", etc. Worked fine. You can always go the insurance route and get 8 tests/months. Best of luck!
It's a reimbursement system, and obviously only applies to people with insurance; so it has its downsides. I filed a claim and it was easier than expected.
This fairly large caveat is worth noting:
> To be eligible for reimbursement, the following must apply...The tests are being used when a person has COVID symptoms or has had direct exposure, and not for school, work, travel, or attending events
This went into effect on January 15, so only applies to tests purchased then or later.
Ah well if it's reimbursement that depends on being able to find them in stock somewhere. FWIW, I found this info on my insurer Cigna's site hidden behind a descriptive "Important Information for Customers" banner, and only accepts the reimbursement form via printed mail despite using online forms for every other reimbursement.