@allonp You are putting your constraint in the wrong place. You want to pull the entire list of GPS Tracking records. That’s the list you will be making a change to each item so you need all the records.
With the constraint you have, Bubble is looking for a GPS Tracking record with a unit_id that matches ALL of the unit_id’s you are bringing in from the API call. It is, of course, returning zero records with that constraint so that is why it appears as though nothing is happening.
Look at it this way, instead of filtering our database records by the API data, we need to filter the API data by our database records.
In the Make changes to a list of GPS Trackings, after your position_text = you will set your API call there as it is only where you have :first item’s position_text you want to change that to :filter:first item’s position_text.
Your filter constraint should be unit_id = This GPS Tracking’s unit_id.
Now, having said that, I would guess you could set up a GET call to the API that only brings in a single record. Then you would simply make that GET call and pass the unit_id to the API which says, just give me this record. That would be the simplest way to do this.