Render order (No sprites or multi cam setup)

Hello all,

First of I am VERY new to unity, scripting, programming and coding - baring this in mind I'm sorry if I make rookie mistakes.

I currently have a 3d scene(environment assets) and a 2d plane(The background image)

I need the background image to be rendered behind the 3d scene even though the 3d scene intersects the background plane.

Ive looked into layers and tags but had no luck.
Ive looked into sprites and havent had any luck there.
Ive tried scripting but I always run into errors which im sure is due to my lack of scripting knowledge.

I come from a graphics background so im used to c4d/photoshop and stuff like that - so this is all a bit alien to me

From what I can see online it seems to be a scripting thing but havent had luck

TIA

 

So this is the shader code that I've found online - Ive had a fiddle with the render type and light mode but all it has done is create a 3d geometry mask that allows for the background image to come through that - which is the opposite of what im trying to achieve

Code (CSharp):

1. Shader "KA/Trans"
2. {
3.     Properties
4.     {
5.         _MainTex ("Texture", 2D) = "white" {}
6.     }
7.     SubShader
8.     {
9.         Tags
10.     {
11.         "Queue" = "Geometry-1"
12.                 "RenderType" = "Opaque"
13.                 "LightMode" = "ForwardBase"
14.  
15.  
16.     }            
17.          ZWrite On
18.              Ztest LEqual
19.              LOD 200
20.         Pass
21.         {
22.             CGPROGRAM
23.             #pragma vertex vert
24.             #pragma fragment frag
25.             // make fog work
26.             #pragma multi_compile_fog
27.  
28.             #include "UnityCG.cginc"
29.  
30.             struct appdata
31.             {
32.                 float4 vertex : POSITION;
33.                 float2 uv : TEXCOORD0;
34.             };
35.  
36.             struct v2f
37.             {
38.                 float2 uv : TEXCOORD0;
39.                 UNITY_FOG_COORDS(1)
40.                 float4 vertex : SV_POSITION;
41.             };
42.  
43.             sampler2D _MainTex;
44.             float4 _MainTex_ST;
45.  
46.             v2f vert (appdata v)
47.             {
48.                 v2f o;
49.                 o.vertex = UnityObjectToClipPos(v.vertex);
50.                 o.uv = TRANSFORM_TEX(v.uv, _MainTex);
51.                 UNITY_TRANSFER_FOG(o,o.vertex);
52.                 return o;
53.             }
54.  
55.             fixed4 frag (v2f i) : SV_Target
56.             {
57.                 // sample the texture
58.                 fixed4 col = tex2D(_MainTex, i.uv);
59.                 // apply fog
60.                 UNITY_APPLY_FOG(i.fogCoord, col);
61.                 return col;
62.             }
63.             ENDCG
64.         }
65.     }
66. }
67.