Thank you for the screenshot of the error! There are a few possibilities as to why this error came up for you, and one of the more obvious reasons would be a cache and cookies issue on your browser. Have you already tried to clear the cache on your Google Chrome browser and then access the app? If not, please try the following these steps.
If this does not work, try to access it on an alternative device i.e. if you’re using mobile, try to access it on desktop, and finally you could also reset your internet.
It is important to try all of the above steps first in cases like this as they can often solve the issue.
If you none of the above has worked for you, the next step would be to contact the developers of the app. I was having a look at our App Store, and I just wanted to confirm - is this the app that you are referring to?:
If so, I have found that they have multiple contact options including their phone number, an email address and their developer website with a chat window. All of these can be found on their listing in our App Store if you scroll down and view the right hand side.
I can see that the app in question is for you to be able to build a mobile app for the store - mobile apps for businesses are a great idea as they can increase your sales due to how easy it can be to shop from an app. Other ways to increase sales include creating an eye catching homepage, adding reviews and testimonials to your store, and make your store easy to navigate with organised product categories. You can learn about all this and more in our Shopify Blog article on ‘Higher Conversions, More Sales’.
Let me know if you have any other questions and I will be happy to help.