The naming ET_
suggests that ET_CUSTOMERS
is a table. You can't treat a table like a structure - you have to obtain a table reference first, then either navigate to an existing row or create a new one, and maybe then you can treat that row like a structure. Please also see this answer which has a similar background.
("Maybe" because tables may also be created based on unstructured types, which leads to really weird situation when combined with the JCo, so you should avoid this.)