Payment IDs are generated on the receiving side if you want to tell someone to send to you and want to track that as being from a certain person. It can be some randomly generated hexadecimal string. You would tell that person to use that payment id so you can look up any payments that get sent to that id and know it is from that person. You don't need to have a payment id to send to your own wallet any coins you just want to be able to use freely. Transaction id is different. It's what happens when you send any coins and want to know the id for looking up on an exchange or verifying in your wallet. So I'm just saying you can just send to your wallet address without a payment id if you are just sending to your wallet.