Hey Eric —
So I believe the option to map custom fields to your extra columns appears after you click the 'import' button.
The problem here is the Beehiiv UI copy is slightly misleading.
The button titled 'Import' makes it feel like it's the final step. I shared this because I was reticent to make that final step, afraid it'd mess me up. But if I'm remembering correctly, it isn't.
I'm not 100% sure, but I think you're good to hit that button to complete the flow.
Odd how something can get fuzzy after only a month.