Thanks for reaching out.
Can you let us know which error message you received? As this context will help us assist you further in this matter. I would suggest attempting to clear the cache on your browser and try to add Order Printer to your store once again. If the error persists, you can try this action on another browser, as for example - if you are using Safari try to add the application on Google Chrome.
Let me know if that does the trick, happy to help out.