If you require Vendors to send you additional documentation, and you choose to do it through Messages as an attachment, you'll need to enable attachments for a message thread in order to allow Vendors to send you documentation.
To do so, please follow the below instructions:
1. From the Messages Tab, click on Opportunity Q&A
2. Either locate the message thread where you would like to enable attachments or click on Start an Opportunity Q&A to start a new thread.
2a. If you are starting a new Opportunity Q&A thread, you'll need to select a Recipient and add a subject line.
3. Click on the toggle next to "Vendor Attachments"
If this is a new thread, you'll need to complete the form and send a message to get the thread started. If it is an existing thread, you will be prompted to confirm whether or not you would like to enable attachments for the thread.