When a user sends an invoice from CORE to QuickBooks Online, sometimes the invoice is not posted to the correct account. This is a limitation from QuickBooks Online. QuickBooks automatically puts invoices in the last A/R account used and it has to be changed manually there.
If you have used the option 'Do not send time details for these invoice types' on the QuickBooks Sync Detail > Sync Settings > Invoices screen, the synced invoice does not hit the intended Services account in QuickBooks, but rather the Other Income account. When you use this option, the invoice received in QuickBooks does not show the service line items (time entries) individually, but rather shows a summary. So sending invoices with this option on always affects the QuickBooks account specified under QuickBooks Income Account and not the CORE Code Service Amount in QuickBooks Sync Detail > Sync Settings > Accounts screen. So you should change the account specified there from 'Other Income' to 'Services'. The setting will be saved for the future invoices too.
For the existing invoice, you should delete it in QuickBooks, remove the mapping in CORE and then resend it with the new setting. Check CORE Help Center for details.