The contraction is only used in America when “have” is a helping verb. - you have done it = you’ve done it - they have gone out = they’ve gone out - we have seen it = we’ve seen it You would almost never hear the helping verb “have” in its full form, in fact; it is nearly always contracted in the spoken language. The example you gave has “have” as the main verb rather than as a helping/auxiliary verb. In this case we never contract it. However, I think they do in England.

In the Present Simple form, the HAVE is the main verb and would not be contracted. However, when speaking, you are unlikely to hear the "H" sound as native speakers usually cut sounds to fit stress timing. It's called elision and it's very common. In written form, you'd never contract it. If you see the 've in written form, it's because it a different tense - Present Perfect (have/has + past participle). In this case, the HAVE is not the main verb, but it is an auxiliary verb (helper), so it is both ok and common to contract it.

That's all OK. some native English "writers" (not speakers) may also use the "it's" abbreviation for "it has" when it is clear that "has" is meant (not is) Like "It's been a long time since we met" But of course most normal is "it's" for "it is" And don't confuse with "its" (= from it...) BB - Basler Biker

If you use this contraction, then it should be followed by a verb in the past, for example: "call me when you've decided what to do".