Maybe a silly suggestions but did you check if it is enabled in properties advanced in that table ?

This is what you mean or? It was already checked…

Yes that was the first to check. 
do you have any project were that rmb is shown? 

Check your supplier setup is complete/not inactive/not Prospect..

@PRODQ I checked the supplier and the status is active:

@JULIAN I just checked another Project, where I created Shop Orders already. The difference to my current project is, that in my project the check boxes for “Authorization Required” are checked and in the old project not. And another difference is, that in the old project the “Demand Code” has the value “Project Inventory” and in my new Project the value “Project Delivery”

Looks like it needs Authorising first then...

@PRODQ Can you explain how to do that?

How about after authorising ? (Getting rid of the tick) 

There will be a Purchase Authorisation rule set up which may be for certain suppliers and/or projects and/or values and/or users.  You should probably get in touch with your Admin or Purchasing supervisor to see who has set the Authorisation up.  The requisition will need to be Authorised by the relevant user.  Rule may require individual to authorise or any one user in a group.  Look on the Purchase Requisition and there will be an Authorisation tab. Details of Authorisation steps/users etc can be found here.

This is the correct action, right? Now I only have to get the rights to run it...

That’s the one!