The subclass isn't showing up after I paid for it.

1.  How long ago did you buy it? Sometimes it can take a little bit for purchases to show up.
2. Did you buy it via the website or the app? The app takes even longer (sometimes days).
3. Go here. Check at the top that your entitlements are in sync. If they're not, there'll be a button to press. If they are, check further down the page to see if it lists you purchase. If not then you might accidentally have 2 accounts. Contacting support can get your accounts merged.

Bought it 5 days ago Bought it on website and it's on one account.

Check out the Content Accessibility FAQ, it might have some useful information for your issue: (https://www.dndbeyond.com/forums/d-d-beyond-general/bugs-support/142100-how-to-access-content-on-d-d-beyond-faq).

Actually I lied it helped

I figured out that you can't  Select the sub class

you obly chose the spells from it after a certain level

unless it's a public one that somone made

thank you for the help

Thank you got it figured out appreciate it.