Facebook Messenger announces policy changes effective 04 March 2020. It aims to drive timely, relevant communication. It will also put a priority on people-initiated conversations. Below are new policy changes:

Standard Messaging Window and One Time Notification
The standard messaging window is within 24-hours after a subscriber’s last interaction. One can send a single reply without message tags. It should be within the standard messaging window. It may include promotional content.
Message Tags
Message tags describe the content of your message. Facebook is reducing the number of message tags from 17 to 4. These are:
- Confirmed Event Update: Details for an event where a subscriber registered
- Post Sale Update: Transaction confirmations, shipment status, order changes
- Account Update: Application status, approvals, suspicious activity, fraud alerts
- Human-Agent: Human responses to inquiries within 7 days
Messages without tags will not be delivered after the standard messaging window. Never use tags on promotional content. Using them out of the approved cases may restrict a page from sending messages.
Subscription Messaging
Facebook encourages business pages to register on Facebook News Page Index (NPI). Only those registered to NPI will be allowed to send subscription messages.
Sponsored Messages
Businesses can send promotional content using sponsored messages. They are subject to ad integrity controls and auction dynamics. This is to ensure that their volume is consistent with the subscriber’s expectations. Facebook Messenger is making changes to protect subscribers against spam and content abuse. This can drive more positive outcomes for businesses.
Implications for Brand Marketers
Marketers should be ready with the coming changes. It’s best to set expectations on response time. Use a short but concise reply. If not yet registered with NPI, apply immediately. Allow extra time for review and approval before the new policies take effect.
A digital agency can help review your Facebook Messenger strategy. In light of these changes, they have the expertise to make sure that one is compliant. They can provide speedy customer support. And could also help one with omnichannel marketing.
Reference:
https://developers.facebook.com/docs/messenger-platform/policy/policy-overview/
https://developers.facebook.com/blog/post/2020/02/27/best-practices-designing-great-messaging-experiences-messenger/