I have used the API to create the project estimate with all line item fields included custom fields, but the estimate is not being created with the fields shown.

We can take the required actions to fix the issue of the project estimate not displaying in the custom fields, Joe. 

Begin by reviewing your API settings to verify that the custom fields are properly mapped in your API request. If the issue persists, I suggest connecting with the developer's team through this page for immediate assistance. 

Here's how:

1. Go to this link: https://help.developer.intuit.com/s/.
2. Choose QuickBooks Online under What do you need help with?
3. Click Ask a Question.
4. Log into your existing Intuit Developer Account or create a new one.
5. Enter your concern.
6. Click Ask.

If you have any additional questions regarding the setup of custom fields in QBO, don’t hesitate to click the reply button.