You and your friend (or second account) will need all of the required linked. Both players will need to use a PC to add each other on epic games. (you can use a tool like CCleaner to clear your sign in after signing out of epic games to sign in with the other PSN account)
Requirements:
1. After linking your accounts to console and PC versions of the game (only one player needs to have the PC version of the game) add your friend on shift (you can only add friends on shift on the PC version of the game [if both players have the pc version of the game it seems you have to add them on the pc version])
2. Have the person with PC version of borderlands 3 send gear to the Shift account of the console player.
3. Profit
Note: There is a limit to how much that can be sent per hour.
You can send more than 5 an hour by sending 1 every 5 min