@rafsana if other drvices are connecting then the issue is limely to be with the phones. Some phones have a setting thst uses mobile data rather then WiFi if that is faster. On iPhones this is called WiFi assist and is on by default go into the mobile data settings scroll down and disable that option which is near the bottom of a long list.
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
