Can anyone help me with a broken shader?

Saturnine

Apologies if this is the wrong place to ask for this, but I was wondering if anyone has any shader knowledge and could help me out with a shader that was working fine until I switched to URP and now it doesn't work?
It's for a crystal ball and it uses a gradient texture to refract anything behind it, the only error I can see (apart from it's just pink now!) is it says: Material does not have a _Maintext texture property. It is required for Sprite Renderer

using UnityEngine;
Shader "Sprites/CrystalBallShader"
{
Properties
{
[PerRendererData] _Color("Tint", Color) = (1,1,1,1)
[NoScaleOffset] _DistortionTexture("Distortion Texture", 2D) = "white" {}

    _RefractionXOffset("X Refraction Offset", Range(-0.1,0.1)) = 0.01
    _RefractionYOffset("Y Refraction Offset", Range(-0.1,0.1)) = 0.01

    _DistortionScaleX("Distortion Scale X", float) = 1.0
    _DistortionScaleY("Distortion Scale Y", float) = 1.0
}

SubShader
{
    Tags
    {
        "Queue" = "Transparent"
        "IgnoreProjector" = "True"
        "RenderType" = "Opaque"
        "PreviewType" = "Plane"
        "CanUseSpriteAtlas" = "True"
    }

    Cull Off
    Lighting Off
    ZWrite Off
    Fog{ Mode Off }
    Blend One OneMinusSrcAlpha

    Pass
    {
        CGPROGRAM
        #pragma vertex vert
        #pragma fragment frag
        #include "UnityCG.cginc"

        struct appdata_t
        {
            float4 vertex : POSITION;
            float4 color : COLOR;
            float2 texcoord : TEXCOORD0;
            float3 normal : NORMAL;
        };

        struct v2f
        {
            float4 vertex : SV_POSITION;
            fixed4 color : COLOR;
            half2 texcoord : TEXCOORD0;
            half2 grabcoord : TEXCOORD1;
        };

        fixed4 _Color;
        sampler2D _CameraOpaqueTexture;
        float _RefractionXOffset;
        float _RefractionYOffset;

        sampler2D _DistortionTexture;
        float _DistortionScaleX;
        float _DistortionScaleY;

        v2f vert(appdata_t input)
        {
            v2f output;
            output.vertex = UnityObjectToClipPos(input.vertex);

            #if UNITY_UV_STARTS_AT_TOP
            float scale = -1.0;
            #else
            float scale = 1.0;
            #endif

            output.grabcoord = (float2(output.vertex.x, output.vertex.y * scale) + output.vertex.w) * 0.5;
            output.texcoord = input.texcoord.xy;

            output.grabcoord.x -= _RefractionXOffset / 2;
            output.grabcoord.y -= _RefractionYOffset / 2;

            output.color = input.color * _Color;

            return output;
        }

        fixed4 frag(v2f input) : SV_Target
        {
            float2 offsetFromCenter = input.texcoord - float2(0.5, 0.5);
            float2 distortionScale = float2(_DistortionScaleX, _DistortionScaleY);
            float distortionIntensity = tex2D(_DistortionTexture, input.texcoord);

            fixed4 c = tex2D(_CameraOpaqueTexture, input.grabcoord + offsetFromCenter * distortionScale * distortionIntensity) * input.color;
            c.rgb *= c.a;

            return c;
        }
        ENDCG
    }
}

}

Hope some one can help, thanks in advance!