If your "send" transaction is showing as "unpaid" like this:
it likely means that you clicked the "save" icon instead of clicking "Pay"... (or possibly that your transaction failed to broadcast to the network, but it should give an error message if that happens).
To correct this, tap on the transaction, you'll see this screen:
Tap the "Pay" button, and you'll be prompted to select the fee etc:
After setting the fee rate to what you want, tap the "OK" button, and you'll be prompted to confirm:
If you're happy, tap the "OK" button... you'll go back to the "Send" overview screen... and after a short delay, your transaction status should change to "Unconfirmed":
If it stays as "unpaid", then it essentially means that your transaction has not been broadcast for some reason and is only stored locally on your android device. Check your network settings (3 dot menu -> Network) and make sure you are connected to servers: