Answer:
iferror(VLOOKUP(Q2,CBFStaff[[Staff ID]:[Name]],2,FALSE), "Invalid Staff ID")
Step-by-step explanation:
The vlookup formula is not given, but let me explain the general concept here,
iferror works typically like an if else statement, its syntax is IFERROR(value,value _ if _ error), if the it sequal to value, value is returned if not, the next argument is returned, so in this case, we will need to replace value with vlookup function and add an else argument like this
IFERROR(VLOOKUP(),"Invalid Staff ID")// now this will set the message if vlookup cannot find the value