Here are some tips to help you figure it out:
1. Double-check your 2.4GHz WiFi password.
2. Ensure your router does not have accessory controls, such as MAC address filtering or parental control.
3. Temporarily lower or disable your router firewall.
4. Consider changing the 2.4GHz WiFi channel to avoid interference.
5. If you are using a guest WiFi network, make sure there are no access control settings, such as restrictions on surfing or emailing.