When I first sent cryptocurrency to a friend in the US, I was very nervous because the transaction took a long time to confirm. Support asked me to provide the TXID, and I didn't even know what that was. I found an explanation here: https://paybis.com/blog/glossary/what-is-a-txid/ , which clearly explains that it is a unique transaction identifier in the blockchain. After that, I was able to check the status of the transfer through the blockchain explorer and make sure that the funds were already in the network. Now I always keep the TXID for my own control and security.