- your app uses Design time Markers so you cannot add any more Markers with code and expect them to display on the map. Use Run time Markers (using the
) to 'create' additional markers
or add more Design time Markers than you expect to ever use. Set the inactive Design time markers to Marker4.VIsible = false until you need them.
- your present code does 'add' more Marker coordinates to your List but you never assign the coordinates to a Design time marker so the new locations cannot display at present. Because you haven't assigned a marker to the coordinates your TextToSpeech will not work for the added locations because it depends on a marker existing.
You can try these Blocks with the example aia you posted.
The additional Blockks will add Runtime Markers .
However the Markers are not persistent, you have to add your own code to 'save' these 'added' locations for the next use of the app. I did not attempt that.
Regarding the NationalParks Tutorial; add the following code to the tutorial and pressing the location marker will 'speak'

Yes, that is all you need to do with a Run time marker. 