Is there a module to support a web commerce portal to support B2B sales?
Sugar has the Web-To-Lead functionality: http://support.sugarcrm.com/Documentation/Sugar_Versions/7.9/Ent/Application_Guide/Web_To_Lead_Forms/
Also, you could use an existing eCommerce platform (eg: Wordpress and WooCommerce) and have it communicate with Sugar over Webhooks: Using Webhooks - WooCommerce Docs
To manage B2B sales in portal, you can use the Sugar CRM customer portal. In portal, using API calls sales can manage. Or you can integrate Sugar CRM with Magento platform to manage ecommerce data.
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