Hey! I'm running into a very specific issue with my character on DNDbeyond. 

I'm playing a multiclassed Artificer (8) Wizard (2). The wizard spellcasting sub-feature "Copying spells" goes as follows: 

Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it.

This means that I, as a MC Wizard, should be able to copy spells higher than lvl 1 into my Spellbook, because "wizard" and "artificer" spellslots are NOT differentiated. So, I should be able to learn "Fireball" for instance, since at a total I can cast 3rd level spells. 

DNDBeyond however does not allow this. When I try to add new spells into my wizard spellbook, 1st level is the highest I can go. I think this is a slight oversight, perhaps an appropriate change can be accomodated in some future patch?

Thanks in advance and I look forward to hearing all of your thoughts!

https://www.dndbeyond.com/sources/basic-rules/customization-options#Spellcasting

Spells Known and Prepared. You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class. If you are a ranger 4/wizard 3, for example, you know three 1st-level ranger spells based on your levels in the ranger class. As 3rd-level wizard, you know three wizard cantrips, and your spellbook contains ten wizard spells, two of which (the two you gained when you reached 3rd level as a wizard) can be 2nd-level spells. If your Intelligence is 16, you can prepare six wizard spells from your spellbook.

Each spell you know and prepare is associated with one of your classes, and you use the spellcasting ability of that class when you cast the spell. Similarly, a spellcasting focus, such as a holy symbol, can be used only for the spells from the class associated with that focus.

If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slots, but only to cast your lower-level spells. If a lower-level spell that you cast, like burning hands, has an enhanced effect when cast using a higher-level slot, you can use the enhanced effect, even though you don't have any spells of that higher level.

As a 2nd level wizard you may only prepare spells up to 1st level in your wizard spell book. The only way you can use spell slots high than that is with your artificer spells or in the case of your 3rd level spell slots, using the Higher Level Cast.

That is not how spellcasting works. Just because you use spellslots to power both classes does not mean spell progression is shared between classes. As a wizard, you can only learn wizards spells appropriate to your wizard level. You are still a level 2 wizard, and you can only put first level wizard spells down in your book.

Think of your two classes as separate characters using the same resources, if it is easier to understand it that way. Just because you know how to sail to Hawaii with a boat does not mean you know how to fly to Hawaii with a plane, even though both modes of transportation uses fuel.