Sim800l Blink's 7 times

I have a problem with Sim800l module. On serial monitor it shows AT command Ok, also it shows the msg. But It can’t send msg. It blink’s continuously 7 times and then stop for some seconds. What’s the main problem ?
I’m using sim800l with Arduino Uno, giving power to gsm via 3.7v external battery.
Kindly help me…

blinking 7 times means your device not getting enough current, pls check your power source. it must 3.7V - 4.2V 2A,but for me it’s only working on 4.2V 2A