Firstly, please make sure that the sent amount is above or equals the transactions minimum. Transactions below the set minimum will not be credited to your account!
Secondly, please make sure that you have sent correct currency to correct corresponding address. If you have sent BTC to BCH address or ETC to ETH address, these payments will not be credited to your account!
Money sent from outside services are validated immediately and the funds will be available once the transactions are verified by the cryptocurrency networks. This is usually happens in 10-30 minutes, but on rare occasions can take a few hours to complete. During this period the amount sent to your account will be noted as "Pending".
You can check incoming transactions by visiting an appropriate block explorer and then searching for your address, where you expect your coins to arrive.
If the transaction and amount is listed here then it's a matter of waiting until it arrives. In case the transaction is based on a coin that was in a recent transaction then it could be considered a low priority transaction. Transfers can take longer if the transaction fee paid was not high enough. If there is no fee at all the transfer can get a very low priority and take hours or even days to be included in a block.
If there is no transaction and expected amount on the list, then nothing was sent to your account. You should check it with the sender.