Based on @Torben’s Send emails with SendGrid post I’ve been looking for a similar notification system using Slack. It’s cheaper than SMS and faster than e-mail. 
Slack has a lot of functionalities regarding notifications.
I’ll just describe two of the existing methods to send notifications:
- using Incoming Webhooks
- using Slack Web API
For both, I will show you a small example of how to send notifications to a specific channel or user.
Incoming Webhooks
This is the simplest way to post messages from apps into Slack as there is no need for authentication. It’s just a simple POST request to a specific URL.
Example:
- Range A1:B3 - mapping between channels/users and Webhook URL
- Range A6:B8 - notification text and the recipient
- Range D6:D8 - POST request and response
Steps:
1- After creating the Slack App you need to create a webhook for each channel and each user that you want to send notifications. In my case, I’ve created a webhook for #general and another one for myself:
2- Fill all manual information as shown on the image above
3- Add the formula that looks up for the correct webhook and does all the magic
D7:
=POST("https://hooks.slack.com/services/"&VLOOKUP(B7,A$1:B$3,2,FALSE);;"{'text':'"&A7&"'}")
D8: (copy-paste formula in D7)
Slack Web API
For authenticating with the Web API you need to use a Bearer Token (more on that below)
If you want to learn more about this: API Authentication Types and How to Use them
Example:
- B1 - Bearer token used for authentication
- E1 - calculated header used in GET and POST request (just for simplicity)
- E2 - GET request to retrieve the list of users. Needed to send notifications to a specific user.
- Range A5:C7 - notification text and the recipient
- Range D5:E7 - used to retrieve the user_id by parsing E2 and filtering it with C7
- Range G5:G7 - calculated body used in GET and POST request (just for simplicity)
- Range H5:I7 - POST request and response status
Steps:
1- After creating the Slack App you will need to go to: Basic Information > Add features and functionality > Permissions
2- In the Scope sub-section, add scope: chat:write:bot
3- Add scope: users:read
3- Save changes
4- Go to the top of the page and click on Install App to Workspace
5- In the new page, proceed with Authorize
6- Copy OAuth Access Token and paste in on cell B1
7- Fill all manual information as shown on the image above
8- Add the following:
A1: Authorization
E1: =PAIR2JSON($A$1,'Bearer '&$B$1)
E2: =GET("https://slack.com/api/users.list",$E$1)
D6: =IF(C6<>"";PARSE(E$2,"$..members[?(@.name=='"&C6&"')].id");"")
E6: =PARSE(D6,"[0]")
G6: =PAIR2JSON(A$5,A6,B$5,IF(B6<>"";B6;E6))
H6: =POST("https://slack.com/api/chat.postMessage",$E$1,G6)
I6: =PARSE(H6,"['ok']")
If everything worked correctly you should have got a message to the #general and also to the slackbot.
Hope this How-to has been helpful for your spreadsheets.
This is my first one so please let me know if you have any suggestion!