Here are some steps for upgrading Hollow Knight for 1.5, which is necessary for the HKMP mod.

I’m on an older 1.5 version

Open your game store and check whether your game has a pending update. Once you update to the latest 1.5 version, continue with the mod installation.

I’m on version 1.4.3.2

To upgrade to 1.5, follow the steps below.

• Steam: Right-click Hollow Knight in the library > Properties > Betas > "None"
• GoG: Open the game settings in GoG and de-select 1.4.3.2 from the list of patches

After the upgrade, if the game runs fine, continue with the mod installation.

Startup issues for macOS users on Steam

After downgrading or upgrading, your game may not start up correctly (OS Error 4294956470). Read the Team Cherry support article.

I want to stay on 1.4.3.2

Staying on 1.4.3.2 is highly unrecommended, because the guide and the public server are both made for the newer versions of the mod. Only do this if you need to, and you’re a technical user that can figure things out yourself. You may not receive support from others if you have issues.

Get the old 1.4.3.2 version of HKMP and manually put it into your Hollow Knight Mods folder, or click the "Manually install mods" button in the old 1.4.3.2 Mod Installer.

If you have the old "Multiplayer Client" and "Multiplayer Server" mods, uninstall them in the old 1.4.3.2 Mod Installer to avoid conflicts with HKMP.