Hi, @Dóra Halász!
This is only available for FB Messenger automations. Here are instructions: https://help.manychat.com/hc/en-us/articles/14281158573852-Messenger-Lists-in-Manychat
Now… If you're trying to do It with Instagram… bad news: https://help.manychat.com/hc/en-us/articles/14281158573852-Messenger-Lists-in-Manychat#:~:text=1.%20Instagram,their%20Manychat%20accounts.
Meta doesn't allow new accounts to get this enabled. 
Hope this helps...
Hi Fabio,
Thank you so much for your quick response. I understand.
Do you have any ideas on how we could still use ManyChat (Whatsapp and/or Instagram) during our conference — before, during, and after the event — to send information to participants?
Hi Fabio,
Thank you so much for your quick response. I understand.
Do you have any ideas on how we could still use ManyChat (Whatsapp and/or Instagram) during our conference — before, during, and after the event — to send information to participants?
With WhatsApp you can always create Message templates to send to your contacts on specific days.
https://help.manychat.com/hc/en-us/articles/14281326740124-How-to-use-WhatsApp-Messages-Templates-in-Manychat
IMPORTANT: there are costs to send Message Templates via WhatsApp. Here you find more info about it: https://help.manychat.com/hc/en-us/articles/14281380243740-WhatsApp-pricing-guide
😉
Thank you very much your help Fabio :)
Well this isn’t true as some of the top manychat content creators that even spoke at the manychat events are using this where they are messaging me everyday outside of the 24 hour window
Hey @Bodydropbrad yes, every account that got on the Beta that Fabio mentions in this article is capable of sending messages outside the 24 hours.
I have several client accounts that were part of the Beta and are making the most of this awesome feature.
Unfortunately, as of right, now the Beta is paused and they’re not enabling new accounts.
So yes, there is a handful of accounts using this feature, and many influencer accounts are in that bunch. But if you’re not in the select group who got in, it’s not available and you can’t use that feature.