Learn English – “I can’t login” or “I can’t log in”

This may reflect your spell/grammar software's inadequacies—it may not recognize these contractions. See our Canonical Post on this subject.

However, if you actually typed these words with initial capitals, it is possible that the software is correct. There is no reason to capitalize these words in the middle of a sentence, and none of these constructions ordinarily appears at the beginning of a formal written sentence. In Standard English only the first auxiliary in a verb group is inverted with the subject: we write Should I have done it? rather than Should have I done it?, and so forth. Even in conversation you rarely hear Shoulda X with a pronoun X, only with fairly "heavy" subjects like or “Shoulda General Eisenhower relieved Patton?” or “Shoulda the Poplar Street Bridge been closed?” Those are colloquial constructions which few grammar checkers are likely to be able to distinguish.

I understand your confusion.

At least in India, both are in practice. However, if you typically go by its Hindi origin 'लाख', the spelling 'Lakh' is proper.

It's worth noting that OALD has an entry for 'Lakh' and not 'Lac'.

[Personally, I prefer/practice 'Lakh'].