The main things that cause "Join Dashpay" to not appear on your mobile wallet are:
1. You have a 32-bit device (only 64-bit devices are supported).
2. Syncing is incomplete. For some users, it is getting stuck at 31 or 33%.
3. A large number of EvoNodes are not working. Restarting the app or waiting can help with this.
4. Internet access is unavailable. This will cause numbers 2 and 3 to fail.
If you continue to have issues after confirming that none of these conditions apply, contact the support desk.