Working with array from Rest API


I am looking for some help. We are trying to build a chat app with Appgyver and Firebase’s Real-time database. However, we ran into an issue. We need to store data as a list of objects apparently since this error has been popping up:

But for whatever reason, we are unable to POST it correctly (we tried everything we could find). It gets stored like this:

May someone suggest a solution how to store data so we can GET the entire collection as an array?

Thank you in advance,