Hello Michelle,
Vendor option, as Raghavendra explained, it is per Vendor selection:
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However, this will not attend your needs.
Via MIRO you can only have 1 Vendor per invoice document, which is the Vendor in the Header.
It is not possible to post one invoice document with more than 1 Vendor.
You can, for sure, use several POs with different Vendors, but, you will have to choose only 1 Vendor to invoice.
Regards,
Carla