When using the Import Wizard to import data into a non-sendable data extension that encounters an error due to the primary key requirement, choosing the "Overwrite" import type is the correct solution. The "Overwrite" option allows the admin to completely replace the existing data in the data extension with the new data from the import file. This type of import does not require a primary key because it does not need to reference individual records for updates or additions; it simply replaces all records in the data extension. Other import types like "Add Only," "Add and Update," and "Update Only" require a primary key to differentiate between records, especially when updating or adding specific records without deleting existing data.
References:
* Salesforce Marketing Cloud Documentation on "Data Management"