Requirements:

a) Bulk upload/download Product Data
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u can import\export products via csv files

b) Images - download from absolute URL
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what is it?

c) Images - Uploaded to FTP server (upto 10 images of size 20 MB each + PDF + Video option)
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wat is it?

d) Images - To link images using CSV (having image name, SKU, Wholesaler Id), to support another option to upload images using FTP.
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wat is it?

e) PDF Packing List /invoice (with store logo) - Customizable
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presents in cs cart

g) Assign each SKU (Warehouse Name, Location, state, zip, name of supplier, shipment duation, Shipment by Supplier/Store)
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currently u can set the company that sells the product, shipment duration - in shipping method.

h) Shipping Label as PDF (Fedex, UPS, USPS)
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wat is it?

i) Notification - PO via email to respective supplier (with attachment, Packing List-PDF, Shipping Labe PDF )
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wat is it?

j) Supplier's area (Download PO, Packing list (pdf), Shipping labels (pdf), Order history, Update Tracking#, Accounting/payment history)
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multivendor has vendor panel. there in order details you can donload packing slip, see orders, update shippings and set tracking for them, see account balance

k) Supplier's area to upload images/product data, FTP to download/upload images, PO data and Payment/Invoice Data)
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vendor can update their product data and set product images also

l) Accommodate various wholesale price model (commission, buying on wholesale price, fix-fee+commission, plus/minus Shipping cost)
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you can create wholesale usergroup and set another price for them

m) Inventory feed via FTP (Suppliers are given FTP account to push inventory feed and marketplace to read fetch and update inventory)
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u can update it via CSV files

n) Will have three instances (Dev/Stage/Prod)....Stage/Prod will have images and we should be able to sync from Prod to Stage.....Will push code from Dev to Prod (prior to pushing, sync Prod with Stage)
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we will use GIT for the development with 3 branches

o) Supplier Interface will use different sub-domain or domain then store front
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will do

p) Supplier Users Management
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presents, if I undertand correctly

q) One SKU submission by multiple suppliers, management.
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wat is it?

A Integration:

A.1 We will push bulk product information from Supplier Interface on nightly basis to Store front
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you need to activate vendor products just at night?

A.2 We will push inventory information on 3 hour interval to Store front from Supplier Interface
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inventory that vendor updated should show at storefront just in 3 hrs?

A.3 Server to run on Linux (php/mysql)??
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yes, we can install nginx + fastcgi server

A.4 We will push our own products and as well as listing from 3rd party suppliers
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wat is it?

A.5 Order will be coming from Store front for further pushing to Supplier area (besides email notification with PDF attachments)
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yes, vendor can see it in admin and will have a notification

A.6 Custom Notifications (Orders, Returns, Customer Support)
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exists

B Confidentiality

B.1 You would sign an agreement that you would not broadcast, publish or list our brand in your portfolio, website, press
release or any other media or medium which shows our company is using your platform/product/services

B.2 Web presence, email notifications would not have any footprint of your product, but use our brand.

C Transition and Backup

C.1 Option to download ENTIRE data for backup purposes
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wat is it?

C.2 Complete export of data for easy transition to other platform
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cs-cart supports export some data to csv, you can check it in ca cart demo

D. Merchant Account

D.1 Option to use merchant account
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isnt it like supplier? cs cart supports just customer, admin and vendor

E. Shipping

E.1 Option to use our Fedex/UPS/USPS account for shipping label printing
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wat is it?

E.2 Print Shipping Label (with no footprint of your product/company/module)
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wat is it?

E.3 International Shipping

E.5 Custom shipping duration based upon each SKU (2 days to 60 days)
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each product should have custom shipping duration?

H. Integration with Marketplaces

H.1 Option to push data to marketplaces such as eBay, Amazon, WayFair,
Overstock, and others
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cscart supports export only to ebay. maybe some companies have modules for other markets, if no, should be developed from zero

I. Sales Tax

I.1 Sales Tax calculation based upon shipper's (SKU's) location
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how should it work?have any api?

J. Customer Support

J.1 Assign Ticket Number/Autoresponder
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you need to have ability for customers to communicate with admin\vendor?

J.2 Email goes to respective Supplier for Support
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wat is it?

J.3 Supplier response to email (email piping) shows in ticketing system

J.4 Trim URLs and Email address and signatures

J.5 Email address of Customer and Suppliers are not shared but Store Front's email address is used.
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wat is it?