Adding suppliers is only available to the QuickBooks Online (QBO) version, spoons77.
This feature is unavailable in QuickBooks Self-Employed and Solopreneur/Sole Trader plans. That said, you can consider upgrading your subscription to QBO. By doing so, you can add your suppliers to the platform.
To learn more about what QBO version suits your business needs, check out this link: QuickBooks Online Price and Pricing.
Then, once you have considered upgrading to QBO, you can refer to this article to successfully enter your suppliers: Add and manage suppliers in QuickBooks.
Don't hesitate to revisit this thread if you have follow-up questions.
