Is there a word for confusing words like 'everyday' with phrases like 'every day'?

I see people confusing words that are compounded from two words with a phrase made from those words. This is easy to do, as they look and sound very similar:

For example:

• "everyday", an adjective, with "every day", which I assume is a prepositional (or adverbial?) phrase.
• "giveaway", a noun, with "give away", a phrase containing a verb.
• "awhile", an adverb, with "a while", a noun phrase.

However, the word "everyday" has a defined meaning in Standard English, and it's different to "every day". My question assumes that the inevitable language change that leads to each pair merging hasn't happened yet.

Phenomena like this sometimes have specific names (like 'metathesis'). Is there a technical name given to this mixup?

Homophones

Whether it's two words or phrases, if their sound similarity is the problem, they are homophones.

See also egg-corns and mondegreens

I can't imagine a case where you would notice this misuse in speech. Rather you would notice it when viewing written words. I may be wrong but I'd bet good money all the examples you gave would sound exactly the same when spoken.

"Wait awhile" vs "Wait a while"
"Everyday is the same" vs "Every day is the same"
"I don't want to giveaway my secret" vs "I don't want to give away my secret"

In view of that, I'd simply call it a mispelling, an orthographic error or a typo.