Thank you for reaching out with your question, Karen. Let me clarify how ACH payment options work within QuickBooks Online (QBO).
QuickBooks enables ACH payment options if you have an active QuickBooks Payments account or have started the setup process, even if it’s not fully completed.
If your customers have the ACH as a payment option, it was enabled by default in your payment settings or invoices, even though you have not finalized the setup for these payments in your account. If you don’t want ACH payments offered, you can disable them from the payment options. Please see the image below for your reference.

When a customer initiates an ACH payment and your QuickBooks Payments account is not fully set up, the payment will remain in a pending or "on hold" status and will not be deposited into your bank account.
QuickBooks sends you messages, like emails or in-product notifications, to prompt you to finish the setup because it has a pending payment that needs to be deposited. The system is trying to tell you, "A customer paid you, but we can't deposit the money until you complete the necessary steps."
This is a security and verification measure. To ensure the funds go to the correct bank account, QuickBooks requires you to complete the setup, which includes linking and verifying your bank account information.
To do that, it's best to contact our QuickBooks Payments Support. They can securely access your account and guide you through the process of completing the setup and releasing the pending funds. They can also check your account settings and help ensure all payment options align with your preferences.
Please leave a reply below if you have further questions or concerns. We'd be glad to help.