How To Fix UD403 - & is an entity type, so insertion is not possible

SAP Error Message - Details

• Message type: E = Error

• Message class: UD - EDM - Enterprise Data Model

• Message number: 403

• Message text: & is an entity type, so insertion is not possible

What causes this issue?

You tried to add a new node to an entity type. This is semantically
incorrect and is, therefore, not allowed. You can refine only data
models, i.e. new nodes can be added only to data model nodes.
The desired operation is therefore not performed.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.