Thanks for posting here, @dp-davidpymmplum,
I want to be sure you're able to sync an app in your QuickBooks Account. Can you please confirm if you're using QuickBooks Self-Employed or the regular QBO product? Any information will help me with your concern.
In the meantime, Tradify is tested to work for QuickBooks Online subscriptions. If you have QBSE, I recommend getting in touch with their support provider to check if they can transmit data for self-employed accounts.
You will see the app supportability and their contact information here: Connect Tradify into QuickBooks Online
Don't worry, if they do not support QBSE, we have several apps available for data transfer from this link. We also have a separate forum called Intuit Developers, where you can find engineers who can help recommend third-party applications to use. Click this link to our website: Intuit Developers Community.
If you have any more concerns about syncing applications with QuickBooks, feel free to post here again. I'll be right here to help you. Have an awesome day!