Retrieve taxonomy terms and use them in a loop

I have the following code which shows a list of other posts within a single post on the front-end. The $postarea is input as a custom text field in the post back-end. This works but I would like to automate it as the $postarea is the just same as the taxonomy term I select for the post, i.e. if the post is about New York I would select ‘New York’ in the taxonomy field and input “new-york” in the custom text field.

I’ve tried setting $postarea to be the same as the taxonomy(s) selected for that post but get error messages about it being an array or object when it is expecting a string. Any help would be appreciated.