Hi fitbitbel,
This is a good question. It's awesome to hear that a client has more than one company and it sounds like they've got both companies signed up with QuickBooks. If so, that's great! I know transferring funds between companies happen and finding the best way to record it is needed for both sets of books. I'm here to help.
When it comes to QuickBooks Online, there isn't method or feature that will allow you to transfer funds from one QuickBooks account to another. Rather, it would be a matter of recording the transfer in both sets of books. There's a help article here in the QuickBooks Community that can help you with this process, broken down into two parts. The first part would be done in the company the funds are being transferred from and the second part would be done in the company the funds are being received to. Here's the article: Transfer funds between companies
Since you mention a client, it sounds like you might be an accountant yourself, but if you're not and you're not feeling certain about those steps, touching base with an accountant is the way to go. They'll be able to shed light on the best steps to take to record this kind of transaction. The My Accountant tab in QuickBooks Online also makes connecting with an accountant easy through a simple invite field to bring the accountant on as a user to that account and with the Find a pro to help button to find a professional to work with.
To add to the other response on this thread, if the client doesn't have two QuickBooks accounts set up but would like to and use the same login credentials, this article can help: Create a new company and add subscriptions.
To have both companies open at the same time, using multiple browser types or one regular browser and one private browser is a good suggestion. This article also has a suggestion if you're using QuickBooks Online Accountant: Open multiple clients at the same time within QuickBooks Online Accountant. Another option to consider is using the QuickBooks Online app for Windows or Mac, which allows you to have multiple tabs open at once so you can have more than one company open. Learn about the app here: QuickBooks App for Windows and Mac: General support
All the best to you!
