Answer incoming call in baresip by pressing enter

im currently having a project to build a portable SIP client using a mr3020, then i found post Here but i face a problem

how do you answer incoming call? i already add 'answer_mode=manual' in my account file, but when i hit enter, nothing happen.

in my router attached usb keypad, flashdisk, and usb sound. everything works fine but i cant answer incoming call without my computer.

thank you in advanced.