You should be able to leave it blank if your W-2 doesn't have one and e-file. Make sure you are not inputting anything into that box if the W-2 doesn’t have anything listed and then submit.
NOTE: Another option that may work, is to delete the W-2 entry and then re-enter it and submit for e-file. Steps to delete it can be found here
How do I delete a W-2? **
This is something new the IRS is testing out for 2018, so not all W-2’s will have one. Please see here
IRS Expands W-2 Verification Code for Filing Season 2018 for more on verification codes on the IRS’s website. Per IRS: "Taxpayers without a verification code on their Form(s) W-2 may leave the verification code box blank in their tax software product."
What if the verification code box on my W-2 is empty?
