After having created a new purchasing organization, the next step is to assign it to both a company code, and a plant, in order to be able to use it within the MM module. Otherwise, some issues may be faced while creating Purchase orders for example.
First of all, go to the customization transaction SPRO, and navigate to Enterprise Structure > Assignment > Materials Management > Assign Purchasing Organization to Company Code
Purchasing organization to company code assignment in SPRO
In the change view, find the Purchasing organization to which a company code should be assigned, enter it, and save
Company code entry for purchasing org assignment
A customizing request will be necessary and a prompt with ask for it
Prompt for customizing request
Then, back in SPRO, navigate to Enterprise Structure > Assignment > Material Management > Assign standard purchasing organization to plant
Assignment of purchasing organization to plant in SPRO
Find the plant to which the purchasing organization should be assigned
Finding the plant to which a purchasing org should be assigned
Enter the purchasing organization, and save
Purchasing org entry for plant assignment
Again, a prompt will request a customizing request