Category "undefined-symbol"

How do i solve "Undefined symbols for architecture arm64" error?

I used the latest version of the AdMob plugin & unity Mediation plugin. but I still get this error, How do I solve the "Undefined symbols for architecture a

why does have in error in undefined symbols?

I'm trying to use a 4x4_keypad.h, LCD_16x2_4bit.h and osc_config.h to get my 4x4_keypad.c, Calculator.c and LCD_16x2_4bit.c cleaner and tidied up. But I get man