RTGS (Real Time Gross Settlement): Real time gross settlement systems (RTGS) are funds transfer systems where transfer of money takes place from one bank to another on a "real time" and on "gross" basis. Settlement in "real time" means payment transaction is not subjected to any waiting period. The transactions are settled as soon as they are processed. "Gross settlement" means the transaction is settled on one to one basis without bunching or netting with any other transaction. Once processed, payments are final and irrevocable.
TT (Telegraphic Transfer) : Telegraphic Transfer or Telex Transfer , often abbreviated to TT, is an electronic means of transferring funds overseas. A transfer charge is collected while sending money. (https://www.caclubindia.com/forum/messages/2009/7/40428_know_payment_methods_in_export_import_trade_.asp?)
LC (Letter of Credit): Letter of Credit L/c also known as Documentary Credit is a widely used term to make payment secure in domestic and international trade. The document is issued by a financial organization at the buyer request. Buyer also provide the necessary instructions in preparing the document.(https://www.caclubindia.com/articles/article_list_detail.asp?article_id=2629)