The following tips may help you solve the problem:
1. Log in to the home router and double-check the 2.4GHz WiFi password. When the Meross app asks for a WiFi password, please make sure that your phone does not enter any unnecessary spaces.

2. Temporarily disable router MAC address filtering, parental control, and restart the router.

3. Move your smart device near the home router, restore factory settings, and reconfigure again.
4. Try another phone.
5. Do not use any WiFi extenders for now.
6. Make sure that the proxy ARP function is not configured on the firewall.
7. If you try to add the device to the guest WiFi, please make sure there are NO access control settings, such as only allowing browsing and sending emails.