Firstly regarding the credits it's one per upload regardless of what you decide to do with that upload afterwards. We have a preview mode in VideoScribe Anywhere so if you want to see what it's going to look like then you would need to use that. As for the purchased credit that does not show there is a 'restore purchases' button on the page where you confirm to buy more so if you have credits outstanding click that and the App will check in with Apple and add anything that has not sync'd correctly.
With the online cloud folder saves there could be a few issues here. VideoScribe gives this error when the save fails and while a poor internet connection but it can also appear generically when a save fails. Sometimes even with a reasonable connection the upload mail fail as it times out and this would be that the combination of internet speed and file size means it could not fully upload in the time allowed. One test would be to create a new scribe, just chuck a couple of library images into it and save that. If this small file works well then there is something specific about the older scribe which is causing an issue.
Please try closing the app, restarting your device, ensuring you have a good internet connection and trying again. If that doesn't work, save your project to your online directory to back it up (this is important) and then try uninstalling and re-installing the app and loading the scribe from your cloud directory (uninstalling the app will remove the locally saved version). The app should show the number of credits you have when you go to render.