Microsoft has recently disabled the "Find as you Type" for Sales Document entry in Microsoft Dynamics 365 Business Central, Version 15.2.X This change was made for performance reasons.
The current advised workaround is to use the ellipse ".." button at the end of the "Customer Name" or "Vendor Name" field to open the lookup list and use the search in the upper left.
The presented guidance for workaround:
- Go to Sales/Purchase Order/Invoices list page
- Create a new Sales/Purchase Order/Invoice
- On the Customer/Vendor Name field press the ellipse “…” to display the list of customers/vendors available.
- From the open List Page, the Search is available.
The alternate solution is to show the related "No." field for the document record i.e. "Customer No." and type to auto search.
To complete the search from the Vendor No. field so the Primary Key of the Vendor No. is used as the base for search. On the Purchase Order, click Show More. Then, from the Vendor No. field, you will complete the search.