ISV 100W + iPhone 15 Pro Max

I bought an ISV 100W sous vide cooker. Pairing with an iPhone 15 Pro Max was unsuccessful. The Wi-Fi was set to 2.4GHz. The encryption was WPA2+WPA3. WPS was off. I tried it in Wi-Fi mode (fast blinking) and AP mode (slow blinking). The device was recognized by the app, but pairing did not occur. The iPhone, ISV 100W, and router were close together.
Only with an older iPad Pro (A2316) was the pairing successful.
What could be the problem here?

If the ISV-100W can connect to the iPad Pro, it means there is no problem with the connection function of the ISV-100W and the network settings of the router. This may be related to the settings of iPhone 15 Pro Max. Please check whether the permissions for the INKBIRD app on iPhone 15 Pro Max are enabled?
In addition, if the iPhone 15 Pro Max is logged into the same INKBIRD app account as the iPad Pro, will the ISV-100W not be displayed on the iPhone 15 Pro Max simultaneously?