I am using the following link from our website using the Simbrief API -
This correctly pre-populates the fields requested (Routes / Dep / Dest etc), however, when the user selects their aircraft type or an airframe, the whole plan automatically recalculates and selects a suggested route, not the ATC route I sent via the API.
Basically, this is because SimBrief considers routes to be aircraft-specific (it may prioritize different ones depending on the aircraft type, props vs jet, etc). So by default it resets them when changing the aircraft type.
That being said, I will add a task to preserve the route if it was sent via an API parameter. Hopefully this will make it into the next update.