There is often confusion on whether successfuly (with one ‘L’) is incorrect or if it’s a British spelling. Which is it?
It’s pretty simple. Successfully is the only correct answer, in all forms of English. Successfuly is not correct, period.
Why the Confusion?
The confusion may arise from the fact that successful ends with an -l. Even though it already ends in an -l, you must still add the full suffix -ly. Thus, successful-ly.
Pretty easy, right?