Well, it seems it is not used in the Present Perfect. "just now" has two meanings: 1. a short time ago: with this meaning it is used in the simple past or past continuous.
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ImladrisDo you have an example with the Present Perfect from a reliable source?No, I don't have a example from a reliable source. I do some research about it. Then come to know that we use "just now" with past simple as you said. But didn't get any answer if we can use it with present perfect. I found one example with present indefinite form.
taruns1008Imladris2. at the moment: with this meaning it is used with the present continuousJohn's in the bath just now - can he call you back?
tamguatlayJohn's in the bath just now - can he call you back?This is fine and natural.
tamguatlayJohn is bathing just now - can he call you back?This is excessively formal.