I’ll selfishly link my Draftist Action Group here 
A pre defined project is not yet possible by default but I’ll add it to my list and will hopefully have some time to update the Action Group in the near future
Todoist made some changes to their api last year that’s why the linked action doesn’t work for labels anymore (I think).
Does your project name include spaces? This often caused problems for me.
If you want to dip into scripting a bit you might want to look into the Todoist object. If it’s always the same project you can script an action that either
- always appends #projectName to the tasks text and uses the quickAdd API to add the task
- or use the standard createTask API with the project id as parameter (you can retrieve that id easily by opening the project in the Webbrowser and looking in the url the project id should be the last part)