We start using your platform and faced a few issues: 

1) If we update a field with an API it is not triggering updates in journeys 

2) According to your documentation, we need "trigger_key" 

to trigger the journey with API, but when we get the info about journeys there is no trigger_key field - only Journey_key and with it it doesn't work. 

3) Journey through your system couldn't go for one lead more than 1 time.

The best way if we can trigger the journey with our system every time we update the contact. 

But it aslo would be ok if your system could notice a change of the field with API and push it into journey

Also, want to notice, journey is set up on filed update