No mapping exists from object type <type> to a known managed provider native type.

var c = new SqlConnection();
TypeMapper.Add<VarcharKey>(DbType.AnsiString, true);

//Working and maps correctly to the `varchar` string 👌
var query = "SELECT * FROM A WHERE A.KEY = @KEY";
await c.ExecuteQueryAsync(query, new { Key = new VarcharKey("key")});


//Not working entirely ❌
var query = "SELECT * FROM A WHERE A.KEY IN (@KEYS)";
await c.ExecuteQueryAsync(query, new { Keys = new VarcharKey[]{ "key" }});

public class A {
public string Key {get;set;} //it's a varchar in the database
}

 internal sealed record VarcharKey(string Value) : IConvertible
    {
        public static implicit operator string(VarcharKey source) => source.Value;
        public static implicit operator VarcharKey(string source) => new VarcharKey(source);
        
        public TypeCode GetTypeCode() => throw new NotImplementedException();

        public bool ToBoolean(IFormatProvider? provider) => throw new NotImplementedException();

        public byte ToByte(IFormatProvider? provider) => throw new NotImplementedException();

        public char ToChar(IFormatProvider? provider) => throw new NotImplementedException();

        public DateTime ToDateTime(IFormatProvider? provider) => throw new NotImplementedException();

        public decimal ToDecimal(IFormatProvider? provider) => throw new NotImplementedException();

        public double ToDouble(IFormatProvider? provider) => throw new NotImplementedException();

        public short ToInt16(IFormatProvider? provider) => throw new NotImplementedException();

        public int ToInt32(IFormatProvider? provider) => throw new NotImplementedException();

        public long ToInt64(IFormatProvider? provider) => throw new NotImplementedException();

        public sbyte ToSByte(IFormatProvider? provider) => throw new NotImplementedException();

        public float ToSingle(IFormatProvider? provider) => throw new NotImplementedException();

        public string ToString(IFormatProvider? provider) => Value;

        public object ToType(Type conversionType, IFormatProvider? provider) => throw new NotImplementedException();

        public ushort ToUInt16(IFormatProvider? provider) => throw new NotImplementedException();

        public uint ToUInt32(IFormatProvider? provider) => throw new NotImplementedException();

        public ulong ToUInt64(IFormatProvider? provider) => throw new NotImplementedException();
    }