Troubleshooting step 1:
Confirm following the steps below if the HTML file extension is added to the list of allowed file types to your website:
- In the persona bar, Settings > Security > More tab > More Security Settings tab below More tab
- At the end of this page, you'll find all allowed extensions written in a textarea called "Allowable File Extensions", check if the HTML extension is there.
- If it's not there, please make sure to add a comma and then the HTML extension at the end of the allowed file type list ( like this ",HTML")
Troubleshooting step 2:
If you do have HTML added to the Allowable file extensions for the website you need to review the HTML Editor Manager configurations as below:
- Go to Host > Advanced Settings > HTML Editor Manager
- Click on 'everyone'
- Expand Document Manager Settings
- Check if any filters are applied (If there are filters applied you will need to add HTML)
Credits: Michael Ayoub