There are many reasons why filament won't get out of the tip, but in this session we will focus especially on the extruder assebly and the hobbed bolt.
Especially for those who start now printing, take care about the way you install the hobbed bolt in your extruder, ( it does not matter which extruder).
When you tight the big gear on the hobbed bolt be sure it can turn loose, tight the lockout in the way that the hobbed bolt is firmly fixed to the gear but can slide a little bit within the side bearing.
it will allow self centering with the idler's bearing and feeding hole.
Do not tight to much the springs, if the hot end is clean and the filament slide inside smoothly the pressure should not be to high.
Be sure the hobbed bolt is clean!
Especially the hobbed bolt made with M3 tap are subject clogging particularly with the 3 mm filament.
you will have to clean it very often with a brass brush ( dremel type is cheap and suitable for the operation).