This is incorrect. Article IV, section 2 makes it clear that slavery is protected, though it goes to some effort to avoid using the word "slave" or "slavery."
Also the section that allows congress to stop the slave imports after 1807 is a tacit indication that slavery was accepted under the constitution.
“tacit indication that slavery was accepted under the constitution.”
Slavery is recognized to exist and is accepted. But if slavery was truly protected, there would have been language in the Constitution prohibiting action against the institution.
No such language is found in the Constitution. Since slavery is not protected by the Constitution, states were free to outlaw the institution. By 1804, all states, North of the Mason Dixon Line, had either outlawed slavery or passed laws that would eventually end the practice in their states.
Outlawing slavery does not absolve a state from the Constitutional requirements of Art IV section 2.