for the last few days i've been reading Sunless Citadel to run my very first campaign as a DM, i have a free account with DND beyond but i had access to the CORE books and the tales from the yawning pool.. in the middle of my lecture all my downloaded books suddenly needed to be purchased in order to continue reading them and yawning pool is no longer available?!?!? 

How did you have access to the books in the first place?

not sure.. i remember once me and some friends discussed running a game a very long time ago using beyond... but nothing ever came of it, we became busy. but how come yawning pools isnt available for purchase even? *Edit* i even checked and wasnt part of an adventure or anything

Were you in a campaign that had content sharing on, and the person sharing the content (or yourself) left?

If so, that would remove access if you yourself didn't own them. 

the first thing i did before starting to read was check the campaigns section (none active) and then i had 2 characters weirdly, a lvl1 and a lvl7. NEVER once played dnd. EVER. so it was weird. i ended up deleting the characters, so maybe thats where i went wrong.

That's peculiar. One of those characters was probably in a campaign with content sharing enabled, which means another player had access to the books you were referring to and you had the ability to basically borrow it. Once you got rid of the characters, the content sharing stopped applying to you.

That's honestly a huge bummer.. I was super excited to run sunless citadel for the first time.. always something stopping me from playing dnd.. the easy answer is to buy them but the hard answer is I'm a broke college student :'(

Well, you still have free access to the basic rules and the Lost Mine of Phandelver. That's everything you need for an epic adventure that takes the party through levels 1-5.

There are also several free adventures on DDB. see my signature for links to a few of them), plus DMsguild has loads, some of which are pay as you want.

If you have the  Monster Manual, or another monster compendium, you could always make up your own adventure. A lot of creatures are free to use, many of the more commonly known ones, so you don't necessarily even have to buy that (I'm not sure how many are available for free, but there's quite a few).

FYI if I remember right, I saw an email that LMoP was going to be given the Legacy treatment soon. I may be remembering wrong though because I was only paying half attention (because I already own it, so meh).

I never saw that email? Wouldn't overly surprise me since TSO is essentially a republication and expansion of it...but I don't remember seeing that email.

Then again, it's not like DDB gets messages out consistently. It's quite possible I was just never sent it...or it was tucked away in the email so I never saw it.

Quote from Linklite >>

I never saw that email? Wouldn't overly surprise me since TSO is essentially a republication and expansion of it...but I don't remember seeing that email.

Then again, it's not like DDB gets messages out consistently. It's quite possible I was just never sent it...or it was tucked away in the email so I never saw it.

 Just checked my trash folder. Confirmed. Oct 6th, LMoP is transitioning to Legacy content. The email was sent on 9/21. They also stated that they will be replacing it with other free adventure content.

EDIT: This info was buried in a rather full info package. The subject line was 'Meet 25 iconic fairy tale creatures with a twist'. Nothing to suggest a mothballing of content in the title. Anyone that doesn't have interest in fairy content might have simply deleted lol.

Quote from Quar1on >>

Well, you still have free access to the basic rules and the Lost Mine of Phandelver. That's everything you need for an epic adventure that takes the party through levels 1-5.

Just to add onto this, there are also plenty of free one-shots like A Wild Sheep Chase or The Missing Sage (the latter of which was created by me). This guide isn't up to date whatsoever, but some of the resources on it are still available so I would recommend checking it out.

No doubt, it's just that sunless had really caught our eye being one of the most popular back in the early 2000's, but I ended up finding a holographic hard cover core set with a dm screen for 90 CAD. Unopened!! :) a good person had helped me by letting me use their copy of sunless, so the adventure is on!!!!

Quote from Linklite >>

I never saw that email? Wouldn't overly surprise me since TSO is essentially a republication and expansion of it...but I don't remember seeing that email.

Then again, it's not like DDB gets messages out consistently. It's quite possible I was just never sent it...or it was tucked away in the email so I never saw it.

 Now it is announced on their front page. Intro to Dragons of Stormwreck Isle will replace it as the free adventure module.

Quote from Erik_Soong >>

Quote from Linklite >>

I never saw that email? Wouldn't overly surprise me since TSO is essentially a republication and expansion of it...but I don't remember seeing that email.

Then again, it's not like DDB gets messages out consistently. It's quite possible I was just never sent it...or it was tucked away in the email so I never saw it.

 Now it is announced on their front page. Dragons of Stormwreck Isle will replace it as the free adventure module.

Huh, it would've been nice to have both available, but I get not wanting to give out half of the new Phandelver and the Lost Obelisk book for free.

Quote from Erik_Soong >>

Quote from Linklite >>

I never saw that email? Wouldn't overly surprise me since TSO is essentially a republication and expansion of it...but I don't remember seeing that email.

Then again, it's not like DDB gets messages out consistently. It's quite possible I was just never sent it...or it was tucked away in the email so I never saw it.

 Now it is announced on their front page. Dragons of Stormwreck Isle will replace it as the free adventure module.

I just read that. Looks like Dragons of Stormwreck Isle won't be replacing it, Intro to Dragons of Stormwreck Isle will. Apparently only the first two encounters will be free.

Whoops! Thank you for the catch!

Quote from BoringBard >>

Quote from Erik_Soong >>

Quote from Linklite >>

I never saw that email? Wouldn't overly surprise me since TSO is essentially a republication and expansion of it...but I don't remember seeing that email.

Then again, it's not like DDB gets messages out consistently. It's quite possible I was just never sent it...or it was tucked away in the email so I never saw it.

 Now it is announced on their front page. Dragons of Stormwreck Isle will replace it as the free adventure module.

Huh, it would've been nice to have both available, but I get not wanting to give out half of the new Phandelver and the Lost Obelisk book for free.

Yeah. Although I won't complain too much if this is the start of a new trend, where all the adventure modules that are lacking in depth get a nice makeover and the old versions are made available for free for a few months before being locked behind the Legacy label.