I'm using two (nrf24L01 + Arduino Uno) nodes to communicate with each other. Serial input from node1 will be sent to node2. A special character 'p' when sent to node2, it will reply that it's available. It is working fine when using arduino ide serial monitor on pc. When I use serial usb app on android to get serial input only the text is sent to another node and the special character sent does nothing and prints like any other message.
I solved this problem by turning off CR+LF and selecting None for newline in send section. CR+LF was adding something extra to my input. By removing that program works fine with Android.
About CR,LF : "Newline is a control character or sequence of control characters in a character encoding specification that is used to signify the end of a line of text and the start of a new one. Some text editors set this special character when pressing the ↵ Enter key." - (Wikipedia)