adafruit fingerprint sensor not being detected

I have wired my fingerprint sensor to my Arduino Leanardo as instructed by the adafruit fingerprint sensor library. the problem is the light is on but I cannot for the life of me work out how to enroll fingerprints into it I have tried the enroll code but it just says that the fingerprint sensor isn't being detected :(. if anyone know how to fix this problem please help me.

fyi i have put left wire to gnd then next to to rx and tx respectively and finally the 4th wire to the 5v hole.

We can't see your code or your schematic.