If you only want to export a few designs with Pinreel and don't intend to export more, it might be more worth it to Pay for a single export.
1) Tap the 'Export' button, from the edit screen.
2) If a design contains premium elements a popup will ask you to export as draft (with watermark), pay for a single export or Go Premium.
3) Export the Video as draft and see if it is what you want. To export as draft does not cost any money, but you will have a watermark on your design.
4) Export the video design again and tap 'Buy single Export'
5) A payment screen will show up and after the payment is complete your export will start.
6) The Payment credit is only used if an export is successful. If you stop the export, you will have one credit which you can use later.