Resolution:
If the intention is to pass this method as a parameter to another method expecting a delegate, then use the keyword METHOD as in the example.
Example:
       class-id a.
       method-id main static.
           invoke M2(M1)             *> Error
           invoke M2(method M1)      *> ok
       end method.
       method-id M1 (s as string) static.
       end method.
       method-id M2 (del as type Del) static.
       end method.
       end class.
       delegate-id Del (s as string)
       end delegate.