Having the option to link additional customers, such as a sponsor, to a single project is indeed a great idea, Aco. It would ensure that transactions related to the project also appear in the sponsor's activity page.

Project-related transactions will only appear on the activity page of the customer you selected when creating the project.

QuickBooks Online doesn't have the option to associate multiple transactions by customer with a single project. However, I acknowledge the value of this functionality in managing sponsors and customer relationships more effectively. I encourage you to share this idea directly with our product engineers.

Here's a sample screenshot showing how you can send your feedback within the Projects page.

I also want to acknowledge your resourcefulness in using the Bill To field on the Invoice page to include the sponsor's name. It's a practical workaround for ensuring proper tracking within the project.

Feel free to leave further questions in this thread. We're always here to help.