Rules to follow:
Basically, if an import job has associated with parameters, then we need to send a manifest or .properties file with the source file as a zip. But if the import job does not have any parameters, then we don't send any manifest file at all.
For example, we have GL daily rates import job which does not have any parameters. So simple a source file is enough to do bulk import to ERP.
Otherside, AP invoice, Supplier or Journal are associated with parameters, thus for them, we need to send .properties file with the source files as zip to do bulk import.