QB Issue Resolution:

If they have made no changes to their file while you have had it, you can make a portable copy of backup copy and send it to them.  They can restore it and be back in business.HOWEVER, if they have continued to enter transactions after they sent you the backup file, all of their data will be gone.

Resolution for Issue 'My client sent me a portable copy of their company file so I could work on their inventory, how do I get the changes to them without them having to manually enter them?' available: Yes (Solved).
Source: Intuit Community forum.

My client sent me a portable copy of their company file so I could work on their inventory, how do I get the changes to them without them having to manually enter them?: 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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