If you're having sign-in issues while trying to login to the Napster app from your Android device, try the following steps to resolve it:
Step 1: Update Napster App manually
To update Napster App using the Google Play Store app on your mobile device:
Open the Google Play Store app.
Tap Menu My apps & games.
Apps with an update available updates are labeled "Update."
Find the Napster app you want to update and tap Update.
Step 2: Password should not contain any special characters
If your password contains any special characters, then you may get this error “we’re sorry. We’re currently unable to reach our server in order to sign you in, please try again shortly”. As a workaround, try resetting your password here without any special characters or follow the instructions given in this Article
Step 3: Turn on CA certification for GoDaddy.com
Open your device's Settings app “Settings”.
Under "Personal," tap Security.
Under "Credential storage," tap Trusted credentials.
Go to System and turn on CA Certificates for GoDaddy.com