This could be a case of either Moonpay scamming you or you not being connected and synched properly with an Electrum server.
If you enter your receiving address on a block explorer such as
https://blockstream.info/ or
https://blockchair.com/, can you see the incoming transaction there? If it's visible there, but not in your Electrum client, it could be just a synchronization issue. If it's shown on a block explorer, does it say confirmed or unconfirmed?
In your Electrum client, what is the color of the ball in the bottom right corner? Green means that it's synchronized, red means it isn't.
Try switching to a different server by clicking on that ball icon to bring up the network settings. Untick the
Select server automatically option, pick a random server from the list, right click on it, and select
use server. If the ball goes red after you switch servers, do it again until you find one that connects and syncs.
