How to stop duplicative messaging app notifications?

My company is no longer supporting Slack, which my team has used to receive notifications from Smartsheet. We are switching to Gchat to receive Smartsheet notifications via a messaging app. We prefer this over email.

I followed these instructions to set up notifications on Gchat, but now I am receiving every notification twice in Gchat

and also twice in Slack.

To try to resolve this problem, I revoked Slack's access via the Personal Settings > Apps per these instructions

and yet I am still receiving notifications there. And duplicative notifications for every one notification on Smartsheet.

The notifications are only appearing once while in the Smartsheet notifications section and I've made no changes to my automations workflows, so I don't believe this to be a duplicative workflow.

Anyone have any suggestion to stop receiving duplicate notifications?

Answers