@CreepersBeCoolSo, first to know: If you had the BF1 CTE inatalled on your Console already and had access to it (not matter if currently deleted or not, cause it's still in your download Library) you should be able to get into Incursions then.
The reson is, the Team shut down CTE on Consoles at all. But they still tested stuff in Incursions(only PC), so later on they released Incursions on Consoles as well.
It is NO new application to download tho, it's simply the last CTE Update we got which turned the CTE into Incursions (also the pic. of the application).
So in that case, if you had access to the CTE already, you'll automatically have access to Incursions as well. Once you have it installed!
Other people who didn't had access before, had to wait for them to open up more registrations slots for it. And currently at this point, there are no new ones.
So that might be the case you could have why it won't let you get Incursions.
Just to know: Registrations could be done through the BF1 Base Game main Menu. Go to the Tab "More" and then "BF1 Incursions"!