Object type & is not defined for message type &

What causes this issue?

A value for object type &v1& was supposed to be read from an IDoc of
message type &v2&. A reference from this object type to a field in this
message type is not mainained in ALE Customizing.
Object values are read from an IDoc in the ALE layer in the following
cases:
- recipient determination (the configurations here are in the
customer distribution model)
- when linking the IDoc with an application object
- when serializing IDocs in application input
- when using lists for master data distribution

How to fix this error?

In ALE Customizing, check your configurations for the options Master
data distribution->Lists, serializing and linking. Furthermore, check
the configurations in your customer distribution model. If they are
correct, maintain the missing object type in ALE Customizing, or
consult your ALE administrator.

Error message extract from SAP system. Copyright SAP SE.