In order to get list of vendors perform /V1/udapi/vendors GET API call. It expect searchCriteria as parameter. More details on how to construct the filter check can be found here http://devdocs.magento.com/guides/v2.1/rest/performing-searches.html

In order to get single Vendor information perform /V1/udapi/vendor/info/:id GET API call. :id parameter could be either vendor entity id or his name.

In order to get list of vendors products perform /V1/udapi/products/:id GET API call. :id parameter could be either vendor entity id or his name. It expect searchCriteria as parameter. More details on how to construct the filter check can be found here http://devdocs.magento.com/guides/v2.1/rest/performing-searches.html

In order to get vendor reviews perform /V1/udapi/vendor/reviews/:id GET API call. :id parameter could be either vendor entity id or his name. It expect searchCriteria as parameter. More details on how to construct the filter check can be found here http://devdocs.magento.com/guides/v2.1/rest/performing-searches.html

In order to get offers from multiple vendors perform /V1/udapi/vendor/product-offers/:sku GET API call. :sku parameter should be product's sku.

Example:

GET http://magento.loc/rest/V1/udapi/vendor/product-offers/24-WB04

RESPONSE

{
    "items": [
        {
            "vendor_product_id": 14,
            "vendor_id": 1,
            "product_id": 14,
            "priority": 1,
            "vendor_sku": "v1-24-WB04",
            "vendor_cost": null,
            "stock_qty": 22,
            "backorders": -1,
            "status": 1,
            "shipping_price": null,
            "vendor_title": null,
            "state": "new",
            "state_descr": null,
            "freeshipping": 0,
            "vendor_price": 46.77,
            "special_price": null,
            "special_from_date": null,
            "special_to_date": null
        },
        {
            "vendor_product_id": 2061,
            "vendor_id": 2,
            "product_id": 14,
            "priority": 2,
            "vendor_sku": "v2-24-WB04",
            "vendor_cost": null,
            "stock_qty": 33,
            "backorders": -1,
            "status": 1,
            "shipping_price": null,
            "vendor_title": null,
            "state": "new",
            "state_descr": null,
            "freeshipping": 0,
            "vendor_price": 49.27,
            "special_price": null,
            "special_from_date": null,
            "special_to_date": null
        }
    ],
    "search_criteria": null,
    "total_count": 2
}

In order to get product questions to vendors perform /V1/udapi/vendor/product-questions/:sku GET API call. :sku parameter should be product's sku. It expect searchCriteria as parameter. More details on how to construct the filter check can be found here http://devdocs.magento.com/guides/v2.1/rest/performing-searches.html

In order to create new question to vendors perform /V1/udapi/vendor/product-question-ask/:id/:sku POST API call. :id parameter could be either vendor entity id or his name. :sku parameter should be product's sku. Other parameters are: name - customer name, question - question text, visibility - 0 / Private or 1 / Public