Our solution has required multiple actions:
1-Adjust the scripts on the SharePoint site as @Amebr Amber suggested https://learn.microsoft.com/en-us/sharepoint/allow-or-prevent-custom-script#to-allow-custom-script-on-other-sharepoint-sites
{This step switched our index file from downloading to opening}
2-Change our sharepoint library settings: (from the root folder on SharePoint) Settings Gear > Library Settings > More Library Settings > Versioning Settings > Requred documents to be checked out before they can be edited = No
{This step straightened out our ability to "check in" files from RoboHelp. Checked out files were not viewable from SharePoint to anyone with SharePoint access other than the person who had them checked out, i.e. I could see it, but my colleagues could not.}
3-In Robohelp, set up collaboration. From the top ribbon menu: Collaborate> Open Connection > select profile > Add project > pick the sharepoint folder where this published project lives. Republish the project. (And possibly return to the collaborate menu which now includes a "check in" option.)
{This allowed me to remove the "checked out" status on the SharePoint files from within Robohelp and to do it all at once. If I tried to check in from the SharePoint side I had to check in all the files in each folder.}
4-Publish the project from Robohelp (to SharePoint).
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