Correct spelling, explanation: stopped is a past simple form, a past participle form, and an adjective participle of the infinitive to stop. It is made of a basis (stop) and a suffix (-ed). This word must contain a double -p letter because of a valid rule in the English language: when there is a single vowel before the last (and stressed as well) consonant in a word, we have to double that consonant. That’s why the correct form is stopped and the incorrect one is stoped.

Definition of stopped:
1. verb (past simple, past participle), to come to an end
When I saw her coming, I immediately stopped talking.
I recently stopped smoking cigarettes.
2. adjective participle, ceased to happen
My car was stopped at the end of the road.
Susan was stopped from seeing her boyfriend.

Collocations with stopped:
Some most commonly used collocations include: suddenly stopped, currently stopped, and stopped dead.

Incorrect spelling, explanation: the most common way of creating regular past simple/past participle forms (and also the adjective participles) is adding a specific suffix (-d or -ed) to an unchanged root (the verb). It’s worth remembering that sometimes we must do one other thing: double the last consonant of the root when there is a single (and stressed) vowel before the last consonant in a word. That is the reason why this word should be spelled as stopped, not stoped.