esp8266 connection; error app

hi guys, greetings.. and sorry for my bad english. hope you'll understand this

i've made an app with app inventor 2, and this app is used for displaying sensors from my project. i use esp8266 as my connection from arduino mega 2560 and my app. i also made a thingspeak channel. but when i open my app, it appears a window error code:

bad arguments to lookup in pairs
the operation lookup in pairs cannot accept the arguments: , [field1], [-1], -