Non valuated material GR

here i have to receive the goods from the customer and i have to give Receipt for that, the material is non valuated, i have to just do job work on that material.

for giving receipt i tried considering the customer as vendor and i made the material as non valuated, and i extended the purchasing view for non valuated material.

i thought of creating the purchase order for that material with separate document type and taking the printout and giving to the vendor(Customer).

But here i am not able to create PO system is throwing this error

Account assignment mandatory for material CxXXXXXXXXX (enter acc. ass. cat.)

Message no. ME062

Diagnosis

There is no provision for value-based inventory management for this material type in this plant. Account assignment is thus necessary.

Procedure

Please enter an account assignment category.