Plug-In Store doesn't have the option for adding / trying plugins (post upgrade 2.6 -> 3.5) Having recently upgraded a dev instance of CraftCMS 2.6 to 3.5, I'm trying to add the plugins via the store.  I can find all the plug-ins I want to add, however there's no option on the page to add / try the plug-in.  I figure I've probably missed something basic.
Anyone got an idea of what I should be looking for here?
(am pretty new to this environment...)
If you look in your config/general.php, you will probably find that you have 'allowUpdates' =&gt; false set for the environment you are trying to trial the plugin on (stage/prod?).
Change that to 'allowUpdates' =&gt; true and you will be able to install what you want.