PriceYak only works with GTC ("good 'til cancelled") listings on eBay and you need to have an eBay store in able to be able to use GTC.
If your listings are not GTC, repricing will work correctly, however when an item goes out-of-stock on Amazon, PriceYak will be unable to pause the listing for you.
PriceYak repricing requires GTC because when items go OOS, PriceYak uses the "0 quantity" eBay feature to prevent sales until the item becomes available again. eBay only allows this feature to be used on GTC listings.
If your current listings are NOT GTC, it is best to convert them to GTC, or end them and relist as GTC.
If your listings are not GTC and go out-of-stock, you will see a red 'X' where in the "Success?" column of the "Revisions" section of your listing's page on PriceYak. This means the item went out-of-stock, but PriceYak was unable to set its quantity to 0 on eBay since it was not GTC. So you could sell the item at anytime even though it is no longer available!