Manage search index Couldn't delete required attributes

Summary:

OM>Index Management for Sales Orders>Index Management page, Sales Order Line or Sales Order, I cannot delete attributes I can only add new ones.

In this case, I do not need to search by Customer PO, I select to delete it, click on the delete button and get an error as per printscreen below:

Are we able to delete only the attributes that we have added? Is this the expected behavior of this functionality?

Thank you for your help.

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24D

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