If you're unable to update download the latest version in Package Manager or the Asset Store (newer versions use Package Manager), locate your Unity Asset Store download folder and delete the old asset package before you try downloading again. If it still doesn't work, try deleting the Archanor VFX publisher folder.

Windows: C:\Users\userName\AppData\Roaming\Unity\Asset Store-x.x (type %appdata% in Run)

This usually happens because Soft Particles are enabled on the Materials. Orthographic Cameras do not support Soft Particles and will render the particles invisible.

The in-game scene selection menu requires you to add the scenes from the asset to the Build Settings. These scenes are usually found in the "Assetname/Demo/Scenes" folder. Select and drag them into Scenes in Build.

This error most often comes from a mesh-emitter type of particle system that has no mesh to emit from. If the 'Shape' module of the Particle System is set to Mesh Renderer, you will have to specify a Mesh from which the particles should emit from.

This may be due to Apply Active Colorspace (AACS) is disabled. Select the effect you want to fix, including all sub-emitters, find the Renderer settings in the Inspector and enable AACS.

Alternatively see this forum post for a tool that lets you enable AACS for multiple particle systems.

Make sure to apply the URP Upgrade package in the Upgrades folder.

If materials are still pink, try updating URP to the latest available version in the Package Manager.

For Unity 2019.4 LTS make sure you are using Universal RP 7.2.0 or later.
For Unity 2020.1 versions make sure you are using Universal RP 8.3.1 or later.

This is often because the Materials in the asset has the 'Soft Particles' setting enabled. In some cases you can fix this by enabling 'Depth Texture' on your Main Camera or disabling the 'Soft Particles' setting on your materials.

Make sure to also enable Depth Texture in your SRP settings which can be found in the 'Edit/Project Settings/Graphics' menu. Keep in mind that 'Soft Particles' does not work for 2D projects that use orthographic cameras.

Yes! Most assets from the Asset Store often use the same license. Read more here or check the EULA.

Most of my VFX assets are designed for 3D, but will work for both types. Keep in mind that some effects use billboards that face a specific way and might not show up in isometric or 2D camera views unless rotated properly. Please note that Layering options is in the Renderer tab of the Particle Systems.

By default there is no such feature, but there are workarounds. Take a look at this forum thread for one way to use particles in a UI Canvas.

Another way to render effects in front of the GUI is to use Camera Stacking (URP Tutorial).