You can upload files using the remote file transfer screen that appears by tapping on the "globe" button.

First, tap on "Remote" and add a Dropbox connection. Then navigate to the target folder.

You can then tap on "Local" and select the files and folders in "Local Files" or "iCloud" that you want to upload.

Tap on the "Upload" button in the bottom toolbar.

To edit files in Dropbox, you need to download them first. This is explained in these entries in the manual:

https://www.textasticapp.com/iphone/v6/manual/lessons/How_do_I_access_files_in_my_Dropbox_account.html

https://www.textasticapp.com/iphone/v6/manual/lessons/How_can_I_quickly_upload_downloaded_files.html

The current version 6.2 of Textastic for iOS does not support Emmet. This will be added in Textastic 6.3 which is currently in beta.

Did you try to select the YAML syntax that's already built-in?

Are you using the Mac version? If you are editing an HTML file, you should be able to just press the Tab key to expand the abbreviation. Or you can use Ctrl-E.

Make sure Tab key expansion is not disabled in the Emmet preferences.

You should be able to use the same keyboard shortcut again to dismiss the preview.

What error message do you get?

You might also want to try to enable the "Debug Log" setting in the connection's settings screen. Tap on the (i) button on the right side of a connection to change its settings. This creates a log file when you try to connect to the server which might help you find out what's wrong.

This is quite interesting. Do you know if there is an SDK for iOS developer available? I've looked, but couldn't find any information.

Ok, please send your name and email address to support@textasticapp.com so I can add you.