Improve the error message when a resource doesnt not exist

[emanuelaepure10]

Please follow the template below and provide at least information for
the first 4 sections

Background and Motivation

A better error message could be included when a resource does not exist: for example 404 message.
For example: calling an item that doesn't exist https://example.com/register/item_1 should be shown the message that the item does not exist, not he 404 message.

Proposed change

Cache the error that the API gives when an item does not exist and shot it in the webapp.

[arantzaetxebarria]

Close the issue as it is implemented in #233