Let me help you create the transaction within the Projects section and create a deposit as well, lapin.

First, create an invoice for the total cost in the Project Center. Here's how:

1. Go to the Projects menu and click the name of the project.
2. Click Add to project in the upper-right hand corner.
3. Select Invoice.
4. Enter all the details in the invoice including the total amount. 
5. Click Save and close.

Second, proceed to receiving the payment and enter the amount that equals to the 30% deposit. Please follow these steps: 

1. Open the invoice and click Receive Payment. 
2. Enter the amount in the Amount received field.
3. Click Save and close. 

Then, follow these steps to check how much of the payment has been deposited:

1. Go to the Transactions tab.
2. Look for the invoice and click on it.
3. Go to the Amount received section. 

You can also use these articles to get more details on how the Projects feature works:

• Set up and use the Projects feature 
• Track income, costs, and profitability by project 

I'll be around if you need additional help when adding invoices and receiving deposits.