Purchase order cannot be created for item &

What causes this issue?

Possible reasons for this include:
There is no purchasing master data or incorrect purchasing master data
(for example, in the purchasing info record, in the source list, or in
the quota arrangement).
Organizational data is missing, for example, purchasing organization
and purchasing group.
There is no master record for the specified vendor.
The specified vendor is blocked (deletion indicator is set).
There is no master record for the specified material.

How to fix this error?

Check your entries. If you are authorized, create the required data.
If you have authorization, cancel the transaction/event and contact
your Purchasing department. Check whether you should create a manual
purchase order or post a goods receipt without purchase order (movement
type 501).

Error message extract from SAP system. Copyright SAP SE.