Hey, ​@michal 

There is no way to send a broadcast in bulk outside the Manychat interface. However, there is a workaround using the Manychat API.

Instead of sending in bulk, you’ll need to send your flow user by user. 

You can achieve this using Zapier or Make.com:

Get subscriber → add a tag → send a flow

There are some other limitations like the requests per second. 

Check all the available Manychat endpoints here https://api.manychat.com/swagger and the documentation here https://help.manychat.com/hc/en-us/articles/14959510331420-How-to-generate-a-token-for-the-Manychat-API-and-where-to-get-parameters

Let me know if this helps