I'll try this. Could the magazine not be engaging the disconnect? The magazine seems to be firmly seated and "clicking" into place, but pulling the trigger doesn't (seem) to do anything - it travels all the way back, but there is no click. Without the magazine seated, the trigger feels different and won't go all the way back.
Anything is possible! The fact that the trigger pulls without clicking seems to indicate the sear hasn't engaged the hammer. I seem to recall one instance in my many attempts where I neglected to lift the sear to capture it under tension under the safety lever. The hammer was floppy. I think I recall being able to get it together but not firing.
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I've done that before--ended up with the strut in the wrong cavity.If you look in the mag well you will probably see the strut hanging there. You should be able to move it while pulling the trigger. The hammer needs to be forward to remove the main spring.
If this is the case, as Chet said, you can manually manipulate the hammer forward from the magwell.