Puppy suddenly won't use indoor patches and pees in apartment hallways

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   taking the puppy outside every hour
2. 2
   putting puppy's pee under or on top of the grass patch so they smell it
3. 3
   carrying the puppy downstairs
4. 4
   keeping outside trips strictly for business without play or eye contact until they go
5. 5
   Integrating training in little pockets all day and during walks
6. 6
   Rewarding the puppy when doing something good like pottying on turf or staying calm
7. 7
   taking her several times for a walk
8. 8
   taking the puppy outside every hour or so and after every meal, playtime, or training
9. 9
   using a camera to check on the dog remotely while away
10. 10
    consulting wiki articles and online community guides
11. 11
    Taking the puppy outside every single time, tracking accident-free days with mobile apps like Oopsie, and relying on consistency until the puppy learns to signal at the door.
12. 12
    Using real grass sod patches placed on a private terrace or inside
13. 13
    Hiding a sod patch under a car covered with a tarp
14. 14
    Consulting local vets regarding parvo risk to see if low-traffic outdoor walks are safe
15. 15
    Tethering the puppy to yourself inside with a leash to monitor movement closely
16. 16
    Taking the puppy immediately to the same boring patch of grass upon seeing sniffing or circling
17. 17
    Restricting outdoor time to just standing in one spot for a few minutes without walks or play
18. 18
    Giving a massive treat party for going outside and cycling back inside to try again later if nothing happens
19. 19
    Staying outside for hours
20. 20
    Taking pee pads with the puppy's urine to the yard
21. 21
    Waking up every three hours to take the puppy out
22. 22
    Taking the puppy out 30 minutes after eating
23. 23
    Placing the puppy back in the crate if it doesn't use the bathroom outside
24. 24
    Going back to basics and keeping the puppy right next to you instead of giving freedom in the house
25. 25
    Keep the puppy in a crate more often and take her directly outside
26. 26
    Stay outside for longer periods (half an hour or more) until the puppy eliminates
27. 27
    Use high-value treats and extreme praise when the puppy goes outside
28. 28
    Tether the puppy to the owner indoors to prevent unsupervised roaming
29. 29
    Use enzymatic cleaners to remove lingering odors from indoor floors

In their words

Unedited, most upvoted first, each linked to the thread it came from.