Hi,
I have to install ArcHydro for ArcMap 10.6.1 (it is the version used by my client and I need to test my developped toolboxes for his environment). I had to desinstall ArcMap 10.8.1 and install 10.6.1 (Advanced). Plus, I have installed the patch required for 10.6.1 and I have enabled (therefore have licences) for all 3 analyst extensions (spatial/3D/Network).
I managed to install the ArcHydro extension (.msi) successfully. Unfortunately, half the tools from the toolboxes are unavailable (broken links) and I seriously don't know what to do...

ANY help would be most welcomed!
Thank you to the ESRI community,
Anne-Marie