COBCH1814 The RETURNING phrase is not allowed with PROPERTY-ID and INDEXER-ID

You must remove the RETURNING phrase from the signature; instead use property-value for the return value in the indexer's getter method. For example:

indexer-id string.
   procedure division using by value idx as binary-long,
                      returning return-str as string.    *> remove this phrase
   getter.
   set return-str to "return-value"                      *> and this line
   set property-value to "property-value"                
   goback
end indexer.