Strptime() argument 1 must be string, not

Hello friends,

We created a new doctype for users to capture transactions using the Data Import Tool in ERPNext.

During the process, we downloaded the template with data so as to guide users. The challenge we have is with the date formats. Upon template download in Excel, we have:

We decided to import the template to see it works, then system gives the below error:

No idea what this means. Please help with possible solutions.

Thank you friends.