Voice prompts for navigation should be heard as you approach one of the turns in the route directions. If the route doesn't have any directions with turns saved with it you wouldn't get any voice prompts though, as it reads the text in the directions. You need to have Voice Navigation turned on in the Navigation Settings and you'll also need to be heading in the correct direction on the route within a set distance from the turn, as voice prompts are generated when you approach a turn. You can change this distance in the Navigation Settings. See the following guide for more on this: How To Navigate A Route Using The Plotaroute App
If your position is constantly off-route, it may be that you have accidentally denied location permisison for plotaroute.com. You can check this as follows:
How Do I get my voice activation to work beyond telling me I'm either "off route" or it's "obtaining a signal"? After that nothing!
DESKTOP TABLET MOBILE
(no app download required)