Item Position Relevant for Proforma Invoice

Dear experts,

In VOV7 I've put D in the filed for Billing relevance (relevant for pro-forma)

But when I try to create the Proforma Invoice with VF01 (I'm sure that the Invoice type is a Proforma Invoice) the system give me the message "The document is not relevant for billing".

Could you help me?

Where am I not right?

Regards

Max