I sent a coin to the exchange. But I forgot the payment id. After a while, does the coin come into the exchange account?
If you send coins to exchange w/o payment ID, the balance of xchange wallet will be increased with amount you sent, but coins won't credited to your xchange balance. Try to contact support and prepare detailed explanations with TX ID, wallet number, amount, mb screenshots, etc. Probably, support will help you.
I sent it to the CREP exchange. However, there is no request for help on this site.
I just PM you the CREP dev contact. Press "Send this member a personal message" in Additional Information, and describe your issue.