When creating a file wither to OneDrive, Sharepoint, Dropbox and FTP, it works perfect in the web and desktop application. When the app is run on a mobile device (Android) I get the same error, not dependant on the service it is trying to create on.
Unable to process template language expressions in action 'Create_file' inputs at line '1' and column '1550': 'The template language expression 'json(decodeBase64(triggerOutputs().headers['X-MS-APIM-Tokens']))['$connections']['shared_ftp']['connectionId']' cannot be evaluated because property 'shared_ftp' doesn't exist, available properties are ''. Please see https://aka.ms/logicexpressions for usage details.'.
Based on your expression I think it's related to Microsoft Flow. This board is more related to PowerApps, so if this is indeed a Flow question, please post it in one of the Microsoft Flow boards, you'll get a faster response there.