If the client files his taxes as accrual based, it is already counted as 2015 income, since accrual based account counts income as of the invoice date

but

if the client files his taxes as cash based, then that payment is 2016 income, cash based reports income on the date received

Resolution for '2015 income issue: 'How do I record a payment that was received for a previous year invoice, being that the client didn’t use QB last year?' available: Yes.

The 2015 income 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 2015 income issue yourself by looking for a resolution described in the article. If it is a complex 2015 income issue or you are unable to solve the issue, you may contact us by clicking here or by using other 2015 income support options.

For more information about resolving issues related to 2015 income in Quickbooks/QBO or to get support for the issue 'How do I record a payment that was received for a previous year invoice, being that the client didn’t use QB last year?', click the link below: