QB Issue Resolution:

This unfortunately does not answer my question. As designed, I am linking my Quickbooks with TurboTax. I had several invoices that I sent at the end of the year, but they weren’t paid until 2019. But TurboTax is recognizing them as income from 2018, and flagging that I am not accounting for all of my income. This seems like this will be a red flag for the IRS.
You are asking about basis.
Accrual basis posts the income as of the invoice date
cash basis posts the income as of the payment date
check the tax form, you should have cash basis marked from what you state.
and reports from QB should also be on a cash basis

Resolution for Issue 'The date on the invoices is marked as when it is sent, rather than when it is paid. Because of this, my self employment income is inaccurate when linked with TurboTax??' available: Yes (Solved).
Source: Intuit Community forum.

The date on the invoices is marked as when it is sent, rather than when it is paid. Because of this, my self employment income is inaccurate when linked with TurboTax??: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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