Attaching a new Templates to an existing Project using API calls

[valeSouza]

I can't find any doc about this subject that could bring me a solution, then here I'm:

I already created many projects using API calls, via Snaplogic and even updated them in the same way, but what doesn't work is the action attachTemplate as below:

this was supposed to add a new Template to a existing project, but when I use PUT passing the update parameters it returns error code 422. 

[Jason_JB]

We're doing this via Fusion, but I think the same approach applies.  We're using "assignCategories".

Just a heads up, I remember we originally wrote this with a different call and it removed existing templates from the projects.