sim 800l module

after uploading the program in arduino.... for at command
and when i type AT in serial monitor
the serial monitor will not respond... blank

after uploading the program

Which program?

and when i type AT in serial monitor
the serial monitor will not respond... blank

The Serial Monitor app sends what you type to the device connected to the selected serial port - whatever that port and device are. The device is supposed to do something, and send a response to the serial port, where the Serial Monitor app reads it, and displays it.

We have NO idea what you have, if anything, connected to the serial port. We have no idea what code is on that device. We have no idea what else is connected to that device, or how.

Do you really expect us to be able to help?

Good day to all! I am newbie in this topic and got interested of what arduino can do. as a newbie, i would like to ask all of you if is it possible for the arduino to become the micro-controller of a wifi vendo machine?i am ordering an arduino now and excited to explore the possibilities of this micro-controller. if you are interested in my idea, please help and contact me here, or in my email, vrichmarketing@gmail.com. thank you and more power to you all!!!...

i would like to ask all of you if is it possible for the arduino to become the micro-controller of a wifi vendo machine?

Yes, if you add the right WiFi shield/chip and write the proper code.