“Thanks but my question was is the system available to create debit note for vendor”

Vendor menu > Enter Bill; change the radio button to a Credit.

But, that is NOT your question or your scenario. You stated this:

“now we start to sell to him another products”

This is now ALSO your Customer. […]

Resolution for 'activity Separate issue: 'We Have a vendor we purchased from him products ,but now we start to sell to him another products what can we do ( we want to create invoices to him ) ….!!!?' available: Yes.

The activity Separate 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 activity Separate issue yourself by looking for a resolution described in the article. If it is a complex activity Separate issue or you are unable to solve the issue, you may contact us by clicking here or by using other activity Separate support options.

For more information about resolving issues related to activity Separate in Quickbooks/QBO or to get support for the issue 'We Have a vendor we purchased from him products ,but now we start to sell to him another products what can we do ( we want to create invoices to him ) ….!!!?', click the link below: