As for a contract, you are correct. A compact is not the same species. The AOC had a perpetual clause, yet each State seceded from it and one by one joined in with the compact, known as the Constitution, as Sovereign States, evidenced by their representatives' signatures. How is it that they could secede from a "perpetual union" to form a government different from what had existed prior to 1787? Who gave them permission to violate the contract and dissolve the government? I know this line of questions is not on the subject of tariffs, however shortly after this event, tariffs became a point of contention to the extent that secession was threatened.
As to tariffs, we’ve had several posts showing secessionists themselves saying that tariffs were not the issue. Do you have any examples of actual secessionists saying that they were seceding due to tariffs?