Hi Sammy2,
Sorry that didn’t work out.
No, I am not with the EC plugin team. I have been using the plugin for numerous client sites. If you are copying html into a single post, you will need to make sure you are on the “Text” tab – not the “Visual” tab – in the editor where you add information about an event. (If you cannot switch to the Text tab – that seems to be part of current issues with the plugin.)
If you want to add a button that is included in all the posts, you need to do that in the Events plugin settings. Path is: ‘Events > Settings > Display (tab on the Settings page)’ and add some button shortcode there. You can either add a button above or below the posts. Scroll down to the “Advanced Template Settings” section of the plugin’s “Display” to see the text field where you can add this type of info.
NOTE, the function to add buttons needs to exist in your theme; if it does not already exist, you will need to create it: a good tutorial is online at: https://speckyboy.com/getting-started-with-wordpress-shortcodes-examples/ (I am not affiliated with this site)
If that is too complicated, you might have success installing a plugin specifically to enable buttons anywhere you want them.