Não recebo alertas no Slack, apenas no alertmanager

Segui todas as configurações descritas para emitir o alerta no slack mas não os recebo. Estou executando o docker num MAC M1.

alertmanager.yml

global:
  slack_api_url: 'https://hooks.slack.com/services/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'

templates:
- '/etc/alertmanager/template/*.tmpl'

route:
  group_by: [app, group, env]
  receiver: 'OPRTS-DEUPETCH'
  group_wait: 15s
  group_interval: 15s
  repeat_interval: 1m

receivers:
- name: 'OPRTS-DEUPETCH'
  slack_configs:
  - channel: '#alerts-testes'
    send_resolved: true
    icon_url: https://avatars3.githubusercontent.com/u/3380462
    title: |-
     [{{ .Status | toUpper }}{{ if eq .Status "firing" }}:{{ .Alerts.Firing | len }}{{ end }}] {{ .CommonLabels.alertname }} for {{ .CommonLabels.app }}
     {{- if gt (len .CommonLabels) (len .GroupLabels) -}}
       {{" "}}(
       {{- with .CommonLabels.Remove .GroupLabels.Names }}
         {{- range $index, $:label := .SortedPairs -}}
           {{ if $index }}, {{ end }}
           {{- $label.Name }}="{{ $label.Value -}}"
         {{- end }}
       {{- end -}}
       )
     {{- end }}
    text: >-
     {{ range .Alerts -}}
     *Alert:* {{ .Annotations.title }}{{ if .Labels.severity }} - `{{ .Labels.severity }}`{{ end }}

     *Summary:* {{ .Annotations.summary }}
     
     *Description:* {{ .Annotations.description }}

     *Details:*
       {{ range .Labels.SortedPairs }} • *{{ .Name }}:* `{{ .Value }}`
       {{ end }}
     {{ end }}

prometheus.yml

global:
  scrape_interval: 5s

rule_files:
  - alert.rules

alerting:
  alertmanagers:
  - static_configs:
    - targets:
      - alertmanager-forum-api:9093

scrape_configs:

- job_name: prometheus-forum-api
  scrape_interval: 15s
  scrape_timeout: 10s
  metrics_path: /metrics
  scheme: http
  static_configs:
  - targets:
    - prometheus-forum-api:9090
    
- job_name: app-forum-api
  metrics_path: /actuator/prometheus
  static_configs:
  - targets:
    - app-forum-api:8080

alert.rules

groups:
- name: OPRTS-DEUPETCH
  rules:
  - alert: 'QUEBRA DE SLO'
    expr: (histogram_quantile(0.90, sum(rate(http_server_requests_seconds_bucket{job="app-forum-api",uri!="/actuator/prometheus"}[1m])) by (le))) >= 0.5
    for: 1m
    labels:
      app: 'api-forum-alura'
      severity: 'critical'
      group: 'OPRTS-DEUPETCH'
      env: 'production'
    annotations:
      title: 'QUEBRA DE SLO'
      summary: '...'
      description: '...'

  - alert: 'ERRO 500'
    expr: (sum(rate(http_server_requests_seconds_count{job="app-forum-api", status="500", uri!="/actuator/prometheus"}[1m]))/sum(rate(http_server_requests_seconds_count{job="app-forum-api", uri!="/actuator/prometheus"}[1m]))) >= 0.01
    for: 1m
    labels:
      app: 'api-forum-alura'
      severity: 'critical'
      group: 'OPRTS-DEUPETCH'
      env: 'production'
    annotations:
      title: 'ERRO 500'
      summary: '...'
      description: '...'

docker-compose.yml

version: '3'

networks:
  database:
    internal: true
  cache:
    internal: true
  api:
    internal: true
  monit:
  proxy:

services:
  ...
  
  prometheus-forum-api:
    image: prom/prometheus:latest
    container_name: prometheus-forum-api
    restart: unless-stopped
    volumes:
      - ./prometheus/prometheus.yml:/etc/prometheus/prometheus.yml
      - ./prometheus/alert.rules:/etc/prometheus/alert.rules
      - ./prometheus/prometheus_data:/prometheus
    command:
      - '--config.file=/etc/prometheus/prometheus.yml'
      - '--storage.tsdb.path=/prometheus'
      - '--web.console.libraries=/etc/prometheus/console_libraries'
      - '--web.console.templates=/etc/prometheus/consoles'
      - '--web.enable-lifecycle'
    ports:
      - 9090:9090
    networks:
      - monit
      - api

  alertmanager-forum-api: 
    image: prom/alertmanager
    container_name: alertmanager-forum-api
    volumes: 
      - ./alertmanager:/etc/alertmanager/:ro
    ports: 
      - 9093:9093
    command: 
      - --config.file=/etc/alertmanager/alertmanager.yml
    networks:
      - monit
    depends_on:
      - prometheus-forum-api

  grafana-forum-api:
    image: grafana/grafana
    container_name: grafana-forum-api
    volumes:
      - ./grafana:/var/lib/grafana
    restart: unless-stopped
    ports:
      - 3000:3000
    networks:
      - monit
    depends_on:
      - alertmanager-forum-api
  ...