There are some security restrictions applied on WIX, and other similar "What You See Is What You Get" web hosting platforms, which prevent your embedded tours from switching to full screen mode.
The restrictions are applied to all the iframe content you add to your website on these platforms.
At the moment, there is no effective way to override this restriction, but there is a workaround you can use.
As it is not possible to switch the embedded content to full screen, you can supply it by the direct link pointing to the embed version of your tour:
The most of WYSIWYG platforms support 'HTML code' blocks, so you can add the link and make it look the way you like. It can be a simple textual link as in the example below, or you can use the image, button or any other element with the link to fit the design of your site.
Here is the code example you can use:
<iframe width='640' height='480' src='https://roundme.com/embed/...' frameborder='0' webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe>
<div align="middle"><a href="https://roundme.com/embed/..." target="_blank">Click to enable the full screen mode</a>
Copy the code to your web page and make all the required changes:
Add the link to your tour. Simply replace the content in src='...' and href="..." by the direct link to embed version of your tour. You can find this link inside the iFrame code you obtain from Roundme. You can find some additional info here.
Update the width and height settings to fit the design of your page.
Replace the 'Click to enable the full screen mode' text, if needed.