Why can't I use the Ren 'Py Sync Server?
This question should be asked to the author of the engine, because their servers are almost always overloaded and the probability of a successful exchange is close to zero.
Therefore, the only effective way is to copy the save files from the game folder on the first device, paste them into some Google. Drive, and then, after launching the game once on the second device (so that save folders appear), transfer save files.
The path on both devices is usually like this:
Android: Phone\Android\data\www.townofmagic.com\files\saves