Toon Shader rendering backfaces black instead of transparent

I finally found a great toon shader that works with URP, but somehow it renders backface as black instead of transparent. Could anyone help me figure out what's causing it?

This is the shader:

 Shader "ChiliMilk/Toon"
 {
     Properties
     {
         // Surface Options
         [HideInInspector] _WorkflowMode("WorkflowMode", Float) = 0.0
 
         //BlendState
         [HideInInspector] _SurfaceType("__surface", Float) = 0.0
         [HideInInspector] _Blend("__blend", Float) = 0.0
         [HideInInspector] _SrcBlend("__src", Float) = 1.0
         [HideInInspector] _DstBlend("__dst", Float) = 0.0
         //[HideInInspector] _ZWrite("__zw", Float) = 1.0
         [HideInInspector] _Cull("__cull", Float) = 2.0
         [HideInInspector][ToggleOff]_AlphaClip("__clip", Float) = 0.0
         [ToggleOff] _InverseClipMask("_InverseClipMask",Float) = 0.0
         _ClipMask("_ClipMask",2D) = "white"{}
         _Cutoff("Alpha Cutoff", Range(0.0, 1.0)) = 0.5
 
         //Stencil
         [HideInInspector]_StencilType("StencilType",Float) = 0
         [ToggleOff]_EnableStencil("EnableStencil",Float) = 0 
         _StencilChannel ("Stencil Channel", int) =1
         [HideInInspector]_StencilComp("Stencil Comp",int) = 0
         [HideInInspector]_StencilOp ("Stencil Op",int) = 0
 
         // Default 
         _BaseMap("Albedo", 2D) = "white" {}
         _BaseColor("Color", Color) = (1.0, 1.0, 1.0, 1.0)
         _BumpMap("Normal Map", 2D) = "bump" {}
         _BumpScale("Scale", Float) = 1.0
         _OcclusionStrength("Strength", Range(0.0, 1.0)) = 1.0
         _OcclusionMap("Occlusion", 2D) = "white" {}
         _EmissionColor("Color", Color) = (0,0,0)
         _EmissionMap("Emission", 2D) = "white" {}
 
         //Shadow
         _ShadeMap("ShadeMap",2D) = "white" {} 
         _ShadowStep("Shadow Step",Float) = 0.5
         _ShadowFeather("Shadow Feather",Range(0.0,1.0)) = 0.0
         _ShadowMinus("ShadowMinus",Float) = 0.0
          [ToggleOff]_EnableInShadowMap("Enable ShadowMap",Float) = 0.0
         _InShadowMap("Shadow Map",2D) = "white"{}
         _InShadowMapStrength("ShadowMap Strength",Range(0.0,1.0)) = 1.0
 
         //Specular
         _Metallic("Metallic", Range(0.0, 1.0)) = 0.0
         _MetallicGlossMap("Metallic", 2D) = "white" {}
         _SpecColor("Specular", Color) = (0.2, 0.2, 0.2)
         _SpecGlossMap("Specular", 2D) = "white" {}
         _SpecularStep("SpecularStep",Range(0.0,1)) = 0.5
         _SpecularFeather("SpecularFeather",Range(0.0,1))= 0
         _SmoothnessMap("SmoothnessMap",2D) = "white"{}
         _Smoothness("Smoothness", Range(0.0, 1.0)) = 0.5
 
         //Ramp
         [ToggleOff]_EnableRampMap("EnableRampMap",Float) = 0.0
         _DiffuseRampMap("DiffuseRampMap",2D) = "white"{}
         _DiffuseRampV("DiffuseRampV",Range(0.0,1))= 0.0
 
         //Rim
         [ToggleOff] _EnableRim("EnableRim",Float) = 0.0
         [ToggleOff] _BlendRim("BlendRim",Float) = 1.0
         _RimColor("RimColor",Color) = (1.0,1.0,1.0,1.0)
         _RimPow("RimPower",Range(0.0,10.0)) = 4
         _RimStep("RimStep",Range(0.0,1.0)) = 0.5
         _RimFeather("RimFeather",Range(0.0,1.0)) = 0
 
         // HairSpecular
         [ToggleOff] _EnableHairSpecular("HairSpecular", Float) = 0.0
         _SpecularShiftMap("SpecularShiftMap",2D) = "white"{}
         _SpecularShiftIntensity("SpecularShiftIntensity",Range(0.0,3.0)) = 1.0
         _SpecularShift1Add("SpecularShift",Float) = 0.0
         _SpecularShift2Add("SpecularShiftSec",Float)= 0.0
         _Smoothness2Mul("SmoothnessSecMul",Range(0.0,1.0)) = 1.0
         _Specular2Mul ("SpecularSecMul", Range (0.0,1.0) ) = 0.5
 
         //Outline
         [ToggleOff] _EnableOutline("Enable Outline",Float) = 0.0
         [ToggleOff] _UseSmoothNormal("UseSmoothNormal",Float) = 0.0
         _OutlineColor("OutlineColor",Color)= (0.0,0.0,0.0,0.0)
         _OutlineWidth("OutlineWidth",Range(0.0,5.0)) = 1.0
 
         // Advanced Options
         [ToggleOff] _ReceiveShadows("Receive Shadows", Float) = 1.0
         [ToggleOff] _SpecularHighlights("Specular Highlights", Float) = 1.0
         [ToggleOff] _EnvironmentReflections("Environment Reflections", Float) = 1.0
         _RenderQueue("Render Queue", Float) = 2000
 
     }
     SubShader
     {
         // Lightmode matches the ShaderPassName set in UniversalRenderPipeline.cs. SRPDefaultUnlit and passes with
         // no LightMode tag are also rendered by Universal Render Pipeline
         Tags{"RenderType" = "Opaque" "RenderPipeline" = "UniversalPipeline" "IgnoreProjector" = "True"}
         Pass
         {
             Name "Outline"
             ZTest Less
             Tags{"LightMode"="SRPDefaultUnlit"}
             ZWrite On
             Cull Front
             Stencil
             {
                 Ref [_StencilChannel]
                 Comp [_StencilComp]
                 Pass [_StencilOp]
                 Fail [_StencilOp]
             }
             HLSLPROGRAM
             #pragma prefer_hlslcc gles
             #pragma exclude_renderers d3d11_9x
             #pragma target 2.0
             
             #pragma shader_feature _USESMOOTHNORMAL
             #pragma multi_compile_instancing
             #pragma multi_compile_fog
 
             #pragma vertex Vertex
             #pragma fragment Fragment
             
             #include "../Include/ToonProperty.hlsl"
             #include "../Include/ToonFunction.hlsl"
             #include "../Include/ToonOutlinePass.hlsl"            
             ENDHLSL
         }
        Pass
         {
             Name "ForwardLit"
             Tags{"LightMode" = "UniversalForward"}
             Blend[_SrcBlend][_DstBlend]
             ZWrite On
             Cull[_Cull]
             Stencil
             {
                 Ref[_StencilChannel]
                 Comp[_StencilComp]
                 Pass [_StencilOp]
                 Fail [_StencilOp]    
             }
             HLSLPROGRAM
             #pragma prefer_hlslcc gles
             #pragma exclude_renderers d3d11_9x
             #pragma target 2.0
 
             // Material Keywords
             #pragma shader_feature _INVERSECLIPMASK
             #pragma shader_feature _DIFFUSERAMPMAP
             #pragma shader_feature _RIMLIGHT
             #pragma shader_feature _BLENDRIM
             #pragma shader_feature _INSHADOWMAP
             #pragma shader_feature _SHADEMAP
             #pragma shader_feature _NORMALMAP
             #pragma shader_feature _ALPHATEST_ON
             #pragma shader_feature _ALPHAPREMULTIPLY_ON
             #pragma shader_feature _EMISSION
             #pragma shader_feature _METALLICSPECGLOSSMAP
             #pragma shader_feature _OCCLUSIONMAP
             #pragma shader_feature _SPECULARHIGHLIGHTS_OFF
             #pragma shader_feature _ENVIRONMENTREFLECTIONS_OFF
             #pragma shader_feature _SPECULAR_SETUP
             #pragma shader_feature _RECEIVE_SHADOWS_OFF
             #pragma shader_feature _HAIRSPECULAR
             #pragma shader_feature _SPECULARSHIFTMAP
             
             // Universal Pipeline keywords
             #pragma multi_compile _ _MAIN_LIGHT_SHADOWS
             #pragma multi_compile _ _MAIN_LIGHT_SHADOWS_CASCADE
             #pragma multi_compile _ _ADDITIONAL_LIGHTS_VERTEX _ADDITIONAL_LIGHTS
             #pragma multi_compile _ _ADDITIONAL_LIGHT_SHADOWS
             #pragma multi_compile _ _SHADOWS_SOFT
             #pragma multi_compile _ _MIXED_LIGHTING_SUBTRACTIVE
             //#pragma multi_compile _ _REQUIRES_VERTEX_SHADOW_COORD_INTERPOLATOR
             //#pragma multi_compile _ _MAIN_LIGHT_CALCULATE_SHADOWS
             //#pragma multi_compile _ _REQUIRES_WORLD_SPACE_POS_INTERPOLATOR
 
             // Unity defined keywords
             #pragma multi_compile _DIRLIGHTMAP_COMBINED
             #pragma multi_compile _LIGHTMAP_ON
             #pragma multi_compile_fog
 
             // GPU Instancing
             #pragma multi_compile_instancing
 
             #pragma vertex ToonForwardPassVertex
             #pragma fragment ToonForwardPassFragment
 
             #include "../Include/ToonProperty.hlsl"
             #include "../Include/ToonFunction.hlsl"
             #include "../Include/ToonLighting.hlsl"
             #include "../Include/ToonForwardPass.hlsl"
             ENDHLSL
         }
          
         Pass
         {
             Name "ShadowCaster"
             Tags{"LightMode" = "ShadowCaster"}
 
             ZWrite On
             ZTest LEqual
             Cull[_Cull]
 
             HLSLPROGRAM
             #pragma prefer_hlslcc gles
             #pragma exclude_renderers d3d11_9x
             #pragma target 2.0
 
             // -------------------------------------
             // Material Keywords
             #pragma shader_feature _ALPHATEST_ON
 
             //--------------------------------------
             // GPU Instancing
             #pragma multi_compile_instancing
             #pragma shader_feature _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
 
             #pragma vertex ShadowPassVertex
             #pragma fragment ShadowPassFragment
 
             #include "../Include/ToonProperty.hlsl"
             #include "Packages/com.unity.render-pipelines.universal/Shaders/ShadowCasterPass.hlsl"
             
             ENDHLSL
         }
 
         Pass
         {
             Name "DepthOnly"
             Tags{"LightMode" = "DepthOnly"}
 
             ZWrite On
             ColorMask 0
             Cull[_Cull]
 
             HLSLPROGRAM
             #pragma prefer_hlslcc gles
             #pragma exclude_renderers d3d11_9x
             #pragma target 2.0
 
              // -------------------------------------
             // Material Keywords
             #pragma shader_feature _ALPHATEST_ON
             #pragma shader_feature _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
 
             //--------------------------------------
             // GPU Instancing
             #pragma multi_compile_instancing
 
             #pragma vertex DepthOnlyVertex
             #pragma fragment DepthOnlyFragment
 
             #include "../Include/ToonProperty.hlsl"
             #include "Packages/com.unity.render-pipelines.universal/Shaders/DepthOnlyPass.hlsl"   
             ENDHLSL
         }
 
         Pass
         {
             //ZWrite On
             //ZTest LEqual
             Name "Meta"
             Tags{"LightMode" = "Meta"}
 
             Cull Off
 
             HLSLPROGRAM
             // Required to compile gles 2.0 with standard srp library
             #pragma prefer_hlslcc gles
             #pragma exclude_renderers d3d11_9x
 
             #pragma vertex UniversalVertexMeta
             #pragma fragment UniversalFragmentMeta
 
             #pragma shader_feature _SPECULAR_SETUP
             #pragma shader_feature _EMISSION
             #pragma shader_feature _METALLICSPECGLOSSMAP
             #pragma shader_feature _ALPHATEST_ON
             #pragma shader_feature _ _SMOOTHNESS_TEXTURE_ALBEDO_CHANNEL_A
 
             #pragma shader_feature _SPECGLOSSMAP
 
             #include "../Include/ToonProperty.hlsl"
             #include "Packages/com.unity.render-pipelines.universal/Shaders/LitMetaPass.hlsl"
             
             ENDHLSL
         }
 
         Pass
         {
             Name "Universal2D"
             Tags{ "LightMode" = "Universal2D" }
 
             Blend One Zero
             ZWrite On
             Cull[_Cull]
 
             HLSLPROGRAM
             // Required to compile gles 2.0 with standard srp library
             #pragma prefer_hlslcc gles
             #pragma exclude_renderers d3d11_9x
 
             #pragma vertex vert
             #pragma fragment frag
             #pragma shader_feature _ALPHATEST_ON
             #pragma shader_feature _ALPHAPREMULTIPLY_ON
 
             #include "../Include/ToonProperty.hlsl"
             #include "Packages/com.unity.render-pipelines.universal/Shaders/Utils/Universal2D.hlsl"
             ENDHLSL
         }
     }
     CustomEditor "ChiliMilk.Toon.Editor.ToonShaderGUI"
     FallBack "Hidden/Universal Render Pipeline/FallbackError"
 }

Shader website: https://unitylist.com/p/106r/URP-Toon