RTK base connection declined due to lack of authorization header. According to NTRIP protocol v2, authorization header must present in server request. YouCORS use basic authorization. Example:
POST /MountPointName HTTP/1.1 Host: am.youcors.com Ntrip-Version: Ntrip/2.0 Authorization: Basic cHJpdmV0Om1lZHZlZA== User-Agent: YC Server/2.0 Connection: close