To display analytic account in sale order go through this given path.

First of all go to General settings -> Users & Companies -> Users -> Technical -> enable Analytic Account option.

Select customer's Analytic account

Go inside customer's form view and select analytic account.

Add customer's analytic account in sale order.

Create sale order and then select customer now to add cutomer's analytic account click on add analytic account button.

To show customer's analytic account in sale order go inside other info tab.