update invoice entity

src/modules/invoice/dto/create-invoice.dto.ts

@@ -40,9 +40,15 @@ export class CreateInvoiceItemDto {
 }
 
 export class CreateInvoiceDto {
+  @IsOptional()
   @IsString()
-  @ApiProperty({ description: 'Request ID to create invoice for' })
-  requestId!: string;
+  @ApiPropertyOptional({ description: 'Request ID to link invoice to (optional)' })
+  requestId?: string;
+
+  @IsOptional()
+  @IsString()
+  @ApiPropertyOptional({ description: 'User ID (required when requestId is not provided)' })
+  userId?: string;
 
   @IsArray()
   @ArrayMinSize(1)