2021 WI 1099-R

I'm currently interring income data and my 2021WI 1099-R does not have a box 16.  Last box is 15.  So on the form, I simply left the box blank?  Seems like the other potential would be to use the Box 2a Taxable amount as the State Distribution amount.   When I left it blank then I got a new dialogue box that says "Let's Verify This Entry"  That makes me think I should enter the Box 2a amount.  I thought the program might take the 2a amount off the form and complete the calculations so I didn't want to add anything, but seems like I should?