Thanks a million to jacob1 for this great idea!
Like many others, I struggled to get this working. Below is a picture of my “all block” solution to sending a push message ('cuz this is Thunkable, right?)
You will notice that the Headers do not include the Authorization parameter. Interestingly, when using the include_player_ids parameter, the API key is not required. One less piece of secure information you do not need to include in your app.
I tried to use the query parameters block, but I kept getting errors so I finally switched to the body block. It is important to note that unlike the query parameters and header blocks, the body block is TEXT not a JSON object, so you need to use the GENERATE JSON FROM OBJECT block to get the body to work correctly.
Happy Thunking!