Both forms are correct. Collectable and collectible are different spellings of the same word. The main difference is that collectable is most commonly used in British English and collectible is preferred by Americans. Both words are pronounced as / (kəˈlɛktəbəl) /. Both words can act as adjectives and nouns. When it comes to meaning, it also overlaps.

Correct spelling, explanation: form most commonly used in British English.

Correct spelling, explanation: form preferred by Americans.

Definition of collectable/collectible:
Adjective: worth and capable of being collected;
My friend is a big fan of collectable Lego sets, he does not let anybody touch them.
My sister grows collectible plants, you would never imagine, but they are worth quite a lot.
Noun: an object that can be collected as a hobby or an investment;
I love vintage hats, I have like twenty already, they are collectables.
My younger brother always had a thing for collectibles, now he is in a baseball cards phase.