Once you have been added as a user, you can connect your Slack to send messages directly from you through Pyn.
Here’s how they do it:
Go to Settings
From the home screen, click on Settings at the bottom of your screen.
Open the Senders page
Inside Settings, select Senders, then click the All tab.Click Add in the top right
Select the blue Add button and choose Add Slack Sender.
Complete Slack authorization
You will be directed to a Slack authentication screen. Click Allow to connect Slack.
You’re done!
Once you've authenticated your Slack sender, you'll be returned to Pyn and see your sender active and ready to use.