When you create a homebrew spell or revise an existing one, you can select class availability in the lower right rectangle under the spell description. For some reason, some homebrew subclasses I've created do not show up in the class availability list. For example, I've created Charm, Cold, and Transgression cleric domains. The Charm and Cold domains will show up, but not the Transgression domain, even though it is currently in My Homebrew Collection ("added").

At other times, a homebrew subclass *will* be visible, and you can select it, but once you save the spell and click on the link to view the spell, the subclass no longer appears under the description along with the other available classes. 

This has left me scratching my head quite a few times, and unable to extend class availability of certain spells to some of my homebrew subclasses. 

 Hello Benz74M,

The intended way to add additional spells as available to the spell list of a subclass is to add them in the "Additional Specific Spells" section of a subclass' information section. You should be able to add the spells you're looking to add by going into those subclasses.

Thank you for reminding me you can add spells to a specific subclass this way. 

It still seems like a bug to me that *some* homebrew classes are listed while others are not when using the class availability box in the spell creation process. Especially for someone that creates a lot of homebrew spells, adding them directly to spell lists in the spell creation process is easier than editing the relevant subclasses every time.

If anything the bug is that subclasses show up at all. Spells should only be on class spell lists.

Update: found out the issue. If your homebrew subclass is published on Dnd Beyond (made public), you can't add the subclass to homebrew spells. The solution was to create a revision of the subclass, add the revision to My Collection, and remove the published one from My Collection. The subclass is now listed as a choice when editing a spell.

But this has lead me to discover another "issue". When adding class availability of a homebrew spell to a cleric subclass, the spell automatically becomes an "Always Prepared" spell, rather than just adding it to that subclass' spell list (i.e. extended spell list). But I understand that RAW, there is no domain-specific cleric spell lists.