Click the green button 'Make a Custom Integration'
Choose Incoming WebHooks
Select the channel that will receive data from the form created on Tilda. If this channel doesn't exist, click Create a new channel, then click Add Incoming WebHooks Integration.
Copy WebHooks URL and switch to Tilda. Below on the same page fine tune the integration by changing the channel, your avatar and so on.
Go to Site settings > Forms > Slack
Insert a WebHooks URL, copied from Slack, into a corresponding field. If you have your own domain or you plan to connect one in the future, set all domains where you plan to place the forms to Additional domains. Click Save.
If you did everything right, the page with the list of receivers, including Slack, will upload to your website.
You will receive a message from Tilda confirming the connection to the channel on Slack specified during the connection process.
Return to the page with the form and open the menu on the Content block. Click Slack. Publish the page. The form is ready.
If something isn't working, please make sure your page opens at the same address as you specified in the form settings.