Currently the REST API (https://www.bricklink.com/v3/api.page) does not support
the cross-site access (CORS or JSONP). That makes it impossible to access the
API from a React app for example and requires a server-side component.
Could you enable the cross-site access by either adding the "Access-Control-Allow-Origin:
*" response header to the API (relatively easy change) or adding JSONP support
(a bit harder and it's an older method for cross-site JS API).