What causes this issue?

You have entered either the company code &V1& or a plant assigned to
this company code. However, the company code either does not exist or
has not yet been configured for materials management.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Ask your system administrator to configure the company code.

Procedure for System Administrators

Carry out the following activities as required:
Create the company code if it does not already exist.
You do this in Customizing for <LS>Enterprise Structure</> in the
activity <DS:SIMG.SIMG_CFMENUSAPCOX02>Define, copy, delete, check
company code</>.
Make sure that a fiscal year variant is assigned to the company code.
You do this in Customizing for <LS>Financial Accounting (Global
Settings)</> in the activity <DS:SIMG.SIMG_CFMENUORFBOBY6>Enter global
parameters</>.
Configure the company code for materials management.
You do this in Customizing for the <LS>Material Master</> in the
activity <DS:SIMG.SIMG_CFMENUOLMSOMSY>Maintain company codes for
materials management</>.

Error message extract from SAP system. Copyright SAP SE.