Dear @Mohiemen,

Then this shows signal strength N/A. 
What does that mean? 
How can I solve? (I attach a screenshot of status page)

The Wireless Signal Quality section is only applicable for the Client, Repeater, Bridge and AP Client Router (WISP Client) Modes.

So it's normal that the signal strength shows N/A when the CPE works in AP mode.

For the issue that the phones/laptops cannot detect the SSID from the CPE510, you may check the points below:

1. Ensure your devices support 5GHz WiFi. Do your phones/laptops detect any other 5GHz WiFi?

2. The CPE510 adopts directional antennas, ensure your phones/laptops are within the wireless coverage.

3. Please ensure your Region is correctly selected, ensure SSID broadcast is enabled, and change different Channels for checking. 

How to adjust orientation of outdoor AP for better signal coverage, https://www.tp-link.com/support/faq/1044/