Hello,
Please refer to the router setup section of this post.
If you have two phones, could you please test:
Turn on the hotspot of phone A, it will work as a 2.4GHz wifi router. Phone A is placed next to the product.
Phone B connects to the hotspot of phone A, and downloads the INKBIRD APP.
Phone B connects to the product as instructed by the app.
If the product can connect to phone B in this test, it means its WIFI function is working. Please recheck the router settings.
This can help us check whether it is a router setting problem, or a device setting problem.