I installed the Apex trigger and spring kit in my SD9VE, Great upgrade, love the trigger...everything is great except now the slide don't lock back after the last round is fired. Any advise? Suggestions?

Make sure that you installed the slide lock lever properly.

Put in an empty mag and pull the slide back and see what the lever does.

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I'm pretty sure you don't have the slide stop spring in correctly. It needs to be all the way over touching the left side pistol frame and the spring arm needs to be under the top side of the chrome locking block.
If you have to remove things and can't pop it in place without taking it apart, go to my post from 11-28-13 (click on my name then go to statistics) titled "SD9VE Apex Trigger = 1 Hot Rocket". That may not be the exact title but it's close. There I list some steps that make take down and reassembly easier.

I checked and double checked and everything seems to be in place, when I insert an empty mag in the slide lever goes up in the lock position.....so I don't know.

Check your pistol grip hand positioning. It may be your thumb ever so slightly bumping up and tapping the slide lock.

Its your slide stop spring...take it out and and make sure its all the in.

mp15.22....This was my 1st thought but he replied back saying he's checked and double checked. That's why my follow up post on a wayward thumb.
If that spring arm is not seated under the locking block one will have this type of problem...how do I know?...Reassembled mine incorrectly on the 1st git go!

Y'all were right , the slide stop spring was just a hair away from the frame....the slide stop was hitting the spring as it came up. Problem solved....Thanks y'all!

Glad to be of help!