The 'Show Full (Flightplan) Form' tab on the 'Prepare Flightplan' screen allows selection of the Number (of aircraft) to be entered on the next page. This number is already set to '1' so presumably the number required is the total number in the group or formation. Changing this number automatically brings up a header note advising that 'The numbers and types of aircraft in the formation must be specified in the 'Extra Information' box with the TYP/ keyword', but neither the app nor the manual make any reference as to HOW to add the additional aircraft. The last time I tried to use this feature (for a simple 'pair' of flexwings) it failed - presumably due to a syntax error of some sort, but I had no way of knowing why it was failing, so had to resort to individual flight plans for each aircraft.

 

Following a re-read of the latest Manual and a Forum search this afternoon, the only information I can find is a reference to adding the (additional) registrations to the 'EXTRA INFORMATION' section by using  'TYP/', (already covered by the header message) but again, no detail as to exactly how to do this or whether / how to advise if any of them are of a different type to the primary aircraft. An example in the flight planning section of the SD Manual would allow you to clarify these points and also show of the correct syntax and would help users massively.