Private homebrew you've createdis shared automatically with other players in your campaign, which means they can use it for their characters, as well as read the page for it. However, my DM is unable to view the page for homebrew I've created, which is annoying. I've checked with 3 or 4 of my fellow players, and they are able to view the homebrew, it's just the DM who can't. Does anyone know what's causing this, and how to fix it?

No, the other players, including the DM, won’t be able to read the description page unless you send them the URL. The other players can only see your homebrews on their character sheets. Since the DM likely doesn’t have a character sheet in the campaign, that’s why they can’t view the homebrew. If you send them the URL for your homebrew they will be able to view the description page.

I should clarify, when I send them(the DM) the URL to a homebrew page, it shows an "Error: 404 Page not Found" for them, as if it's not shared with them. When I share a link to a fellow player, they can see it normally.

And they are the DM of the DDB campaign, and your character is in the campaign? And the DM is logged into DDB at the time?

I have several characters in their campaigns, and they have a character in one of mine. I am able to access their homebrew on my sheets, as well as the page(through URL).

Then they might need to re-sync their entitlements here: (https://www.dndbeyond.com/account/marketplace).

It seems to be working now, thanks!

Happy to help.