Hi,
Setting up heparing as a ligand is likely the best choice, as it is typically highly sulfated and we currently have no support for sulfonated glycans (the list of supported ones is here HADDOCK Web Server - Settings). See for example this topic Recognition problem after glycan sulfation
For supported glycans there is a new tutorial describing the best docking protocol (in that case using HADDOCK3): Protein-glycan modelling tutorial using a local version of HADDOCK3 – Bonvin Lab
Cheers,
Marco