Can't override OpenApiSchema

.WithOpenApi(
                opts =>
                {
                    OpenApiParameter? sourcesParameter = opts.Parameters[0];
                    sourcesParameter.Description = "Sources";
                    sourcesParameter.Schema = new()
                    {
                        Type = "array",
                        Items = new OpenApiSchema
                        {
                            Type = "string",
                            Enum = new List<IOpenApiAny>()
                            {
                                new OpenApiString("value1"),
                                new OpenApiString("value2")
                            }
                        }
                    };

                    return opts;
                }