Billing type &1 is not assigned to order type &2

What causes this issue?

Billing type &V1& assigned to order type &V2& does not exist. The
reason is an incorrect assignment of billing type &V1& for
order-related billing within order type &V2&.

System Response

Order type &V2& cannot be assigned.

How to fix this error?

Make sure, order type &V2& is checked in Customizing. A valid entry
must exist in the field <LS>order-related billing type</>.
If necessary, select a different order type.

Error message extract from SAP system. Copyright SAP SE.