You also can get Rocket League credits from the online trading website-LOLGA

Credits can be used to
buy RL items such as a player banner or a rocket trail and blueprints to unlock other items. We'll teach you how to earn credits in Rocket League for free via external trading platforms as well as the in-game store.

You also can get Rocket League credits from the online trading website. Lolga.com is the place to go for Rocket League Trading. You can post trade requests on the website or in the app, but it's better if you join the LOLGA Discord channel and do so there. Discord is generally the fastest way to get an answer.

You can only trade with players on the same platform as you, however, because of Rocket League's cross-progression, you can see your tradeable items from any platform. Unreleased Blueprints, things acquired from the shop, and extra gifts are among the items that cannot be traded. Similarly, you cannot exchange credits for credits or for free credits.

Once you've located a trade partner, get on the same platform as them and invite them to your Rocket League party. Then Select Invite to Trade after selecting the player. A countdown will begin once both players have added and confirmed their trade items. During the countdown, you can still cancel the deal. You'll have your new items after it's finished.