In the case when an order for one domain was created by several people, registration will be carried out only for the first one to pay the bill.
For example, your domain has not been previously renewed and was put into deletion queue. So you wait until the domain removed from registry, and decide to create an order for registration. You create an order, but you didn’t pay immediately (the Internet turned off, you realized that there was no money on the credit card or simply got distracted). Tomorrow, you finally paid the bill - and registration failed. After checking, you see that the domain is already registered.
That's because someone else in this period of time also created an order for domain registration - but paid for it right away. All other requests for registration of this domain when they are executed will be rejected, and the funds will be returned to the your personal account.