NestJS can't resolve a service dependency

I am trying to inject a ContentsService into a SlackModule so that I can use some of the Content functions in my Slack Controller.

This is app.module

@Module({ imports: [ ContentsModule, ZapierModule, SlackModule, ], controllers: [AppController], providers: [AppService], }) export class AppModule {} 

Here is my Contents Module:

import { Module } from '@nestjs/common'; import { MongooseModule } from '@nestjs/mongoose'; import { ContentsController, ZapierController, SlackInteractiveController } from './contents.controller'; import { ContentsService } from './contents.service'; import { ContentSchema } from './content.model'; @Module({ imports: [ MongooseModule.forFeature([{ name: 'Content', schema: ContentSchema }]), ], controllers: [ContentsController, ZapierController, SlackInteractiveController], providers: [ContentsService], exports: [ContentsService], }) export class ContentsModule {} 

This is my Slack Module:

import { Module } from '@nestjs/common'; import { SlackService } from './slack.service'; import { SlackController } from './slack.controller'; import { ContentsService } from '../contents/contents.service'; @Module({ providers: [SlackService], controllers: [SlackController], imports: [ContentsService], }) export class SlackModule {} 

And my Slack Controller

import { ContentsService } from '../contents/contents.service' @Controller('slackevents') export class SlackController { constructor(private contentsService: ContentsService) {} 

But when I run this code, I get this error:

[Nest] 75628 - 05/22/2020, 7:08 AM [ExceptionHandler] Nest can't resolve dependencies of the ContentsService (?). Please make sure that the argument at index [0] is available in the ContentsService context. +44ms\

What is it that I am doing wrong?