Amazon have been sending regular emails to announce that they are upgrading the Product Advertising API (i.e. PAAPI) to version 5 from version 4.
This will happen on the 9th March 2020. After this date, version 4 of the PA API will no longer be available. That means any plugins, apps or services that are not upgrading will stop working.
Here are some upgrade guides to help you if you are not sure:
If you have any questions, just drop a message to support and we will be happy to help you.