Hank here from Shopify.
As this is not a Shopify website, I would not have the specific information on who to contact about this error. Although from your screenshot it looks like the developers were notified of the event.
I checked now for you though and the website loaded up for me, so it may have just been a temporary issue.
From the website, they have a support chat setting, so this may be used to contact them if you are able to view the website. Although I could not find their contact information, this is a link to their help center which you should hopefully get some value from.
If you are referring to one of their apps on the app store, however, I do see they list a contact email of firstname.lastname@example.org, so this may also be of value for you if experiencing an issue with an app rather than a website.
All the best, Hank