Your iPhone must be on your home Wi-Fi (not mobile data), the same network as the spa.
The spa's Balboa BWA Wi-Fi module must already be set up on your Wi-Fi with the spa maker's app. Tubline cannot set up the module's Wi-Fi.
Check the module's address in your router's list of connected devices: look for "BWGSPA" or a device whose MAC address starts with 00:15:27. It can change after a router restart.
Allow Local Network access: Settings → Privacy & Security → Local Network → Tubline.
If the spa maker's app is open on another phone, close it and try again: the module serves only a few connections at a time.
“This is not a spa Wi-Fi module”
Something answered at the address you entered, but not a spa module. Check the address in your router's device list, or use "Find my hot tub automatically".
“The spa did not confirm the change”
The spa ignores some changes while it is priming after power-on, while its panel is locked, or when a set temperature is outside the current range (High or Low). Check the spa's panel, then try again.
The water temperature shows “—”
After power-on the spa has no reading until its pump has run for about a minute. Tubline shows the temperature as soon as the spa reports it.
Can I use Tubline away from home?
No. Tubline talks to your spa only on your home network and has no cloud service, so there is no account, subscription or server involved.
Restore Tubline Pro
Settings → Restore Purchases, signed in with the same Apple Account. Refunds are requested from Apple at reportaproblem.apple.com.
Privacy
See the privacy policy. Tubline has no account and no server; nothing leaves your home network.