The course used to accept a form such as 'move', but we found that people were then gettting mixed up, as mizimano says, with nouns and command forms of verbs, so we now stick with forms like 'to move' and 'moving':
- symud - moving, to move
- Symuda!; Symudwch! - Move!
- symudiad - (a) move; (a) movement
A dictionary usually distinguishes between them by adding various abbreviations after each form to clarify them, but Duo cannot do that.
This is explained in a few places in the course notes.
In the Duolingo Welsh course, expected English translations for Welsh verbnouns are usually "to VERB" and "VERBing" but not "VERB" on its own, because that could be confused with the command form (imperative) -- "Move!" would not be Symud! in Welsh -- or with a noun. (For example, chwarae is not "play" as in "a play" in a theatre.)
So to prevent confusion with this command form, use either "to move" or "moving" when asked to translate symud on its own.
In a sentence, of course, choose the translation that makes sense in English, e.g. Does dim rhaid symud would be "There is no need to move" and Dw i'n symud would be "I am moving".
Remember also that the hints you see when you hover over or tap on a word are not "suggestions" or "recommendations", and not all of them my apply to the current exercise.
So it should not be surprising if some of the hints are not accepted as an answer.
(The list of hints is global and are attached to the word itself, without regard to the sentence that you are currently seeing, thus it may also contain translations that are not appropriate for the current exercise.)