IF THIS SOUNDS LIKE YOU, THEN THIS IS WHAT WORKED FOR ME
Little backstory first, I was dealing with this same issue today after getting a replacement LG G4 from a warranty claim. It was on build VS98613B Android 5.01 Lollipop. I could see the update but when I tried to download it, it would fail quickly with "error 409: update 24C required". Even contacting Verizon Tech Support we couldn't get it to take. Factory Reset didn't change anything. PC Update Assistant would detect version VS98619B but would show "up to date" and grey out the upgrade now option. The pleasant and friendly tech opened, and passed along a support ticket for their networking group to look at. And recommended I wait a few days and try again.
I'm here to tell you why that won't work and what will!
Why it won't work:
You didn't update to Marshmallow when it came out. Totally fine, and plenty of reasons to support why you didn't. HOWEVER. The latest update is a Marshmallow security update. You are on Lollipop still. The update actually needs the 24C update because that was the update designed to carry you over to Marshmallow 6.0 from Lollipop 5.01. This new update can't do that. (at least it appears not to). So how do you get the 24C update now that the OTA update on your phone only detects the recent one? That's exactly what I figured out. And it's really easy everyone. YAY!!!
What will work!!!:
Here's what you do....
First) Go to Apps --> Settings --> Date & Time
Second) Unselect "auto-date & time" checkbox
Third) Manually set Date to: March 1st, 2016
Fourth) Confirm Date by exiting to home menu, Then drag down notification bar. (If it didnt take, try again and be sure to click the arrow back to settings. A quick restart my be required but mine didn't)
Fifth) Go to Apps --> Settings --> System Updates
Sixth) Check for system update
Seventh) Download and Install update
You should now be downloading update 24C!!!! Let it install once it's downloaded. (Be sure to have sufficient battery or plug into charger)
If everything goes correctly, then you will be prompted that you successfully updated to Marshmallow. A quick check of android version should reveal you are now 6.0 and software version "VS98624C". If it shows that then you are now ready to get the latest update 25A!
Just follow the first step then RE-SELECT the "auto-date & time" checkbox. Once the date and time has reset to current, go check your update system again and you will get prompted for the newest update. Download and Install and you have done it my friends!! Congrats and welcome to Marshmallow!
Why it works:
From what I can gather, the OTA System Update can only see the most recent update version for that date in time. But by setting the date and time to AFTER the 24C release but BEFORE the 25A security updates. You forced the OTA System Updater to check for updates NO LATER than that date and time. Since 25A was released just recently, it can't update you to it. So by default, 24C was the only update your phone could go to.
If this helped you, reply to it so i know
On your post you said you were on a pretty early build of Android. 11A I think? Did you try going back to an even earlier date? From what I can tell, 19B is required to go to Marshmallow just as much as 24C is. So perhaps you need to set the date to anything prior to when the marshmallow update hit. I think the first marshmallow update was early Febuary so maybe try January? My date was to receive the 24C update but you may in fact need the final Lollipop update first. Just thinking outside the box based on what worked for me. Might be worth a shot. Let me know if you get any success.
Earliest date I can go back to in Dec 30 2015. If I go before that, it tells me I need to connect to network to check for updates..
Dec 30 still tells me I'm up to date..
(Is there a way I can post a screenshot to show you?)
Ah I see what you mean. Mine says the same thing if I set the date back that far also. The Verizon update servers must have a cutoff period. But that, in theory, should have been early enough back though to get the 19b update. Have you tried the PC update assistant program? (perhaps while having the clock set back). Also might be tedious but worth a try, raise the date up by a couple of days and check for update again. Keep trying every 2 days until you reach March. If still nothing then you may be out of luck getting the update OTA.
I then don't have much other advise other than a less ideal method of installing a different recovery, finding the update you need need online, and manually flashing it. It's definitely not advised if you've never done anything like that. Easy to mess things up, and likely would break any warantees you have on your phone.
My method was to trick the phone into accessing the Verizon OTA update server at a particular time when the update needed was available. It seemed to woek, and I was able to systematically download 24c then 25a. You may need an update prior to 19b that perhaps isn't accessible now due to a server date cutoff.
Best of luck. Hope it triggers for you.
Is there somewhere in Verizon I can contact and have them push ota update to my device?
date switching didn't work
(will have a PC with Internet on the 14th)
From the pc program I can see the 25c update which downloaded, I'm not sure if I should flash as a: can 25c be flashed over 11a? (It didn't give option for other versions and b: many people I see are having problems with the update breaking their phone..
I successfully updated with update tool to vs98613b when it was finished it told be I should wait cause there is another update.
Now when I connect to program, starts with saying "status upgrade available" then when it checks device information it says up to date.
OTA having same issues, changing date still doesn't work.
After update, auto rotate stopped working!!!
I tried a couple ways to test and the accelerometer won't recalibrate (tried in settings, tested in service menu..)