QB Issue Resolution:

if the customer has a credit, and in company settings, advanced, automation you have apply credits automatically that may be the issue, QB is doing what you told it to do and paying the invoice

also check the amount due, it can not be zero or QB thinks it is paid

Resolution for Issue 'When I create a new invoice, It already shows as paid.' available: Yes (Solved).
Source: Intuit Community forum.

When I create a new invoice, It already shows as paid.: 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.

Support for already
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!

Error Recovery for already [Canada]
E-Tech is the #1 Quickbooks data migration and Conversion service provider.

Get 50% off Quickbooks Online

Click Here for 50% off!

Additional Support Options: