Hell
I have been embedding vimeo videos ( iframes) historically on sub albums in html mode successfully until recently.
I now get 403 forbidden when i try to save a new vimeo embed in a sub album (embed code is wiped from the editor)
(NOTE: The embed works fine if I embed on a page but not an album)
I can't see anything in error log that seems to relate to this.
I unchecked some depracated code in the depracated plugin, still no change.

Older embeds on old albums are working but I haven't tried resaving the album in case I lose them.
Any ideas on my next level of troubleshooting?
An upgrade is needed soon but I hoped there may be a way around this for now?

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What do you mean with html mode? The tinyMCE editor html mode? Check the configuration you are using for it and also the allowed tags option in general. Nothing has changed in this regard.

If you want to use external videos I would recommend to use the textobject plugin. https://www.zenphoto.org/news/using-external-sources/

Hello thanks for the quick response, Yes I am using
The tinyMCE editor html mode.
We have the class-video plugin (the theme is now quite old)

Then I can only assume that you are using a tinyMCE configuration that clears iFrames or the allowed tags do. I am not aware of any changes otherwise.