Some of the functions of the geoAPI use rest services. They can also be used in an independant way, give a valider refering URL.
The documentation has moved here:
https://apiv4.geoportail.lu/proj/1.0/build/apidoc
https://apiv4.geoportail.lu/proj/1.0/build/apidoc/tutorial-fulltextsearch.html
https://apiv4.geoportail.lu/proj/1.0/build/apidoc/tutorial-geocodeapi.html
https://apiv4.geoportail.lu/proj/1.0/build/apidoc/tutorial-reversegeocodeapi.html