You should create an income account for timely discounts and use that.

You could use the customer income discount account, but it will skew that account value, a customer discount reduces total income.  A vendor timely payment discount increases total income.  Just not the thing to do.

Resolution for 'already one issue: 'What account I can use to track vendors discounts (early payments). I have already one for customers as income.' available: Yes.

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

For more information about resolving issues related to already one in Quickbooks/QBO or to get support for the issue 'What account I can use to track vendors discounts (early payments). I have already one for customers as income.', click the link below: