I went to purchase $20 worth of RP using my mobile phone, thinking that I had the full $20 on my phone available, not realising that I instead had $19.75. Anyway, it went through the purchase, got to $15 and stopped. Is there any way I can use this for a different transaction? Or do I have to put the extra $5 credit onto my phone to continue?

Would very much like a response.

You would have to put an extra $5 on your phone.
Sorry for the inconvenience.

And if I don't put the extra $5 on my phone in 24 hours the transaction cancels and I lose $15 instead of being refunded or using it in a different transaction?

Let's put it this way.

You can't just put money on your LoL account and use it to buy RP.
You have to buy it in complete intervals in order to complete the transaction and get the RP.
If you try to put on $20 and only have $19.75 it will either cancel your order or keep the RP on your account and you will be banned for "chargeback" and will have to wait until you pay it back.

I hope I cleared things up for you summoner

Also, if you need any further account related support I suggest submitting a support ticket which can be found here.
http://support.leagueoflegends.com/a...s_requests/new

i went to purchase $20 worth of RP using my mobile phone, i type PIN ,and enter the game. so my RP not change, i go webiste check,he tell me ：Oops, you already have a payment being processed.
You can resume the current payment or start a new payment



should i keep waiting? Is anyone getting this same issue?