Incorrect spelling, explanation: specialy is an incorrect spelling, because the core adjective is special, which with adverbial suffix -ly gives form specially. We do not skip any l, this consonant doubles, so the correct form is specially.

Correct spelling, explanation: because of the fact, that the adjective special ends with a consonant l, and to create an adverb we need to add suffix -ly, then l will double in specially. This is also why the form specialy is incorrect. When we add suffix -ly to adjectives ending with l, this consonant isn’t dropped, so specially is the correct form.

Definition of specially:
adverb, uniquely
Rooms in our hotel are specially designed to meet all your expectations.
Using specially developed systems, our services are of the highest quality.