Not pairing

When Sonoff is kept in pairing mode (quick green light is blinking), when attempting to pair, the blinking light goes off. Thereafter, unable to pair. The same Sonoff was earlier working fine. Now, for 4 pieces, I am having the same problem and am unable to pair. These sonoffs are 3 years old. Is there any validity for cloud/functional server support? I have ordered a new one, that is working well on the same application.