QB Issue Resolution:

there is no sales rep list in QBO, so no you can not

gear>feedback and report/suggest it to the developers

Resolution for Issue 'is there a way to designate my salemen to a particular customer so he gets commission on a paid invoice?' available: Yes (Solved).
Source: Intuit Community forum.

is there a way to designate my salemen to a particular customer so he gets commission on a paid invoice?: 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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