If the error "The item cannot be listed or modified. The title and/or description may contain improper words, or the listing or seller may be in violation of eBay policy." is stopping a listing from going live, one of the more common issues is a large gap between prices of variation.
eBay policy dictates that two variations of the same item cannot have a price difference of or more than 4x.
If you look at the eBay listing page (found by going to Manage Listings and clicking on the eBay integration in question) you should be able to find the listing with the error.
Click Edit to take us to the parent listing.
Here we can click Variations and we can see the pricing of all variation listings.
In this example you can see that one of the listings, the lowest, is set at $12 and the highest is set at $50. This is a violation because the difference between those two variation costs is more than 4x.
I can edit one of the listings to change the price. In this example we're going to edit the highest priced item. Clicking save changes will cause the listing to sync again and should resolve your error.