Set up a SharePoint Online site collection as follows:

• Sign into Microsoft 365 as an administrator 
• Click Admin, then Show All, then SharePoint, then Policies, then Access Control.  Confirm that “Apps that don’t use modern authentication” is set to “Allow access”.  If not, you will need to set this to “Allow access”, which might take several hours to propagate to all users. 
• Click Sites, then Active Sites 
• Click Create, then select Communication Site (NOT Team Site), making sure that "sites" is in the final URL rather than "teams", and type in the site collection name (e.g., "Opportunities", "RFP Opportunities", etc.) and select a Group Owner 
• If you wish for RFP Response Builder to auto-create SharePoint sub-sites for each new sales opportunity – or want to allow users to manually create their own sub-sites – modify permissions for the "Edit" permission level, which is the level for SharePoint site "members", so that the following are checked: 
  • Create Subsites 
  • Manage Web Site 
  • Add and Customize Pages 
• Add all appropriate users to the "Members" group of the created site collection 

 
If you’ve already set up a site but are not sure that it’s the correct kind of site (namely a “Communications Site” or “Team site (classic experience)”), the SharePoint administrator can check the site type as follows:

• Log into Microsoft 365 and click “Admin” 
• In the left-hand bar, click “Show all” 
• Under “Admin centers”, click “SharePoint” 
• Select “Sites” then “Active sites” 
• Ensure that the “Template” column says “Communication” or “Team site (classic experience)” and NOT “Team site”