thanks to ALL for the responses. so many!
I don’t know what “select itsu” means. If you type “itsu” you’re going to get いつ. Are you talking about the little っ? You normally get that by typing the double consonant, as you did with yokka = よっか. If you ever need to type っ by itself (which you don’t here), you can get it by typing “xtsu”.
I think it probably means using the kana table and clicking on the small tsu located in the table, which is a possible method of getting the character if typing it out doesn’t work.
thanks . I’ll use that. it seems the issue may be my typing also. fast but sloppy.
It may look like itsu but it’s actually a lowercase L. So, ltsu and not itsu
Why though? That’s terribly inefficient compared to just typing the consonant a second time.
Agreed, unless (of course) the っ is the first kana in a word. (But even then… って comes out just fine with ‘tte’.) I think it’s only really useful for producing manga/light novel style strings of っっっっっっっ. (Ok, again, nope… I literally just typed that by repeatedly hitting ‘t’) Depends on the IME, I guess?
Also a Japanese tip.
ありがとう is not used for “thanks in advanced” or something like that. However, よろしく「おねがいします」is 
Are you on an iPhone or a Mac? I use the hiragana input on my iPhone and I get the little っ by typing つ and then hitting the same button that makes か into が and so forth. On Mac, it’s the same as everyone is saying. Hit the following consonant twice and it pops right up. 
Oh I am such nit wit. I have been typing Japanese for 3 years hitting “ltu” every time that I need a っ. This is so much easier just making a double consonant!
Any time you want a small letter you can also type x before it.
xtu っ
xyu ゅ
xyo ょ
xya ゃ
xi ィ
xe ェ
xa ァ
xo ォ
xu ゥ
Hmm
You do? Generally “ltsu” doesn’t work on WaniKani, because WK treats L as being R. It works for other IMEs, though.
Or maybe “ltsu” does work, but stuff like “li” to get ぃ does not. I can’t say I’ve checked recently.
This is a very confusing thread.
OP did you manage to get the WK IME to work properly?
I also use Mac and iPhone with WK and haven’t had issues with using WK, only when I’ve forgotten to disable the computer’s IME and even then I realise because the word converts to kanji rather than staying hiragana.
as others have mentioned, wanikani does convert the latin characters by itself. So you may want to change to standard latin input while you answer questions on Wanikani. 
sorry for any confusion this caused. I have resolved the problem
thanks. I figured it out. it was my typing
What was the problem in the end? Did you press enter after every letter or something?
was reading l as an I ( i).
my bad.
but I will say that entering double consonants works on some words buy not on others so I will type in ltsu all time hence
Whicj words did you find it did not work on? I can’t really think of ever having that issue, typing in WK or not.