Hello @NeilE53. I apologize that this is happening to you. When you are pasting copied text from another source, like a website or a online document, it can bring over some hidden problematic formatting which can cause you to not be able to edit the formatting of the text in the editor. I recommend first pasting your text into a simple text editor such as Notepad (if you are using a Windows computer) or TextEdit (if you are using a Mac). Here is a link to an article that provides some more information. Let us know if you have any more questions!
Caitlin M. Community & Social Media Support
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