Foreign key & after & is not a key extension

What causes this issue?

For performance reasons, synchronous maintenance of matchcodes from the
database interface of the SAP System is subject to certain
restrictions which the system checks when update type 'S' is selected
for a matchcode ID. For example, a matchcode ID that is to be
maintained synchronously may contain only tables that are
<LS>hierarchically</> dependent on one another. Table A is hierarchally
dependent on table B if the key of A forms a prefix to the key of B,
that is, fields are simply added to the key of the referenced table in
the dependent table (it is also possible for both tables to have the
same key).
<LS>Example</>:

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

The key of table A consists of the fields K1 and K2. In this case,
table B, which is dependent on table A, can only be included in the
matchcode ID if the key of B starts with K1 and K2.

System Response

The system checks the restrictions described here and issues an
appropriate error message.

How to fix this error?

Include only those matchcode object tables in the matchcode ID which
do not violate the restrictions or check your relationship definitions.

Error message extract from SAP system. Copyright SAP SE.