I've been trying to make a new character (fighter) for an upcoming campaign, but when I went to chose a subclass, the dropdown menu only showed one option: Champion. I though it was a bug, so I tried looking at my other fighter from a one shot (Eldritch Knight) and found that the only subclasses available were Eldritch Knight and Champion. I looked at other classes as well, and the problem presided. Only Thief on Rogue, only Fiend on Warlock and so forth. Does anyone know what this is or how to fix it?

It's because you don't own any content on DNDBeyond. The books aren't free IRL and so neither are they free on DNDBeyond. Only one subclass from each class is free because they are in the basic rules.

You either need to purchase the subclass you want to play from DNDBeyond - the entire book that it's in - or have it shared with you via a campaign with someone who has a Master Subscription.

my DM has a Master subscription and I've downloaded all of his shared resources, including Xanatar's, Tasha's, and Eberron, but my race and subclass options are still limited. I have a hero subscription for the unlimited character creation because I like to create *maybes,* and I own many physical source books. but I can't access any options that come with my DM's shares, even within his campaigns... I *did* gain access to more race/subclass options in his Icespire campaign, but he had to manually select the Gloom Stalker subclass in his new campaig (even though I downloaded all sources he owns/shares). I just wanna build some backup chars in case we need to hire mercs, please help!!

It sounds like the DM did not enable content sharing or has reached his maximum limit.

Quote from MysticMuhurune >>

my DM has a Master subscription and I've downloaded all of his shared resources, including Xanatar's, Tasha's, and Eberron, but my race and subclass options are still limited. I have a hero subscription for the unlimited character creation because I like to create *maybes,* and I own many physical source books. but I can't access any options that come with my DM's shares, even within his campaigns... I *did* gain access to more race/subclass options in his Icespire campaign, but he had to manually select the Gloom Stalker subclass in his new campaig (even though I downloaded all sources he owns/shares). I just wanna build some backup chars in case we need to hire mercs, please help!!

 It sounds like you’re trying to make characters outside of the campaign your Dm set up. You can read all the books, but using the content for character creation is limited to the campaign. So a character in the campaign has access. A character outside the campaign does not. 

I whipped up a placeholder for my players to experiment with. They can make and deleted characters in it to see what works. 

as previously stated, this problems happens even when creating a character within his campaigns. as in, log into campaign first and create char thru that. he still had to manually select my subclass, and for our previous Icespire campaign I had the same issue when trying to create a Warforged. he had to change something on his end, but whatever he did last time didn't work this time. so he just created the char I wanted and I claimed it and added the flavor text.

I did not realize there was a sharing maximum on the Master accounts, that might the issue. I know it's nothing on my end at this point

i hate that fact because in real life you can get info from the books without buying them

or from members in your campain

plus that just puts a paywall in front of creativity

and finally, you dont need to be realistic  

But I bought Tasha's and Xanathars. I still have no access to the subclasses I want to try. I dropped my subscription cuz money is tight for me. Did that make it so I can't use my already previously purchased content?!

Quote from MachBuster >>

But I bought Tasha's and Xanathars. I still have no access to the subclasses I want to try. I dropped my subscription cuz money is tight for me. Did that make it so I can't use my already previously purchased content?!

 

 
No. Assuming you purchased them here on D&D Beyond then you should have access. However, if you bought through the app it takes up to 24 hours to update. If you bought on the website it should be instant.

You should also check your entitlements are in sync. From your profile icon choose Account then Licenses or use this link: https://www.dndbeyond.com/account/licenses

Quote from Cyb3rM1nd >>

Quote from MachBuster >>

But I bought Tasha's and Xanathars. I still have no access to the subclasses I want to try. I dropped my subscription cuz money is tight for me. Did that make it so I can't use my already previously purchased content?!

 

 
No. Assuming you purchased them here on D&D Beyond then you should have access. However, if you bought through the app it takes up to 24 hours to update. If you bought on the website it should be instant.

You should also check your entitlements are in sync. From your profile icon choose Account then Licenses or use this link: https://www.dndbeyond.com/account/licenses

(Ngl you saved me.)