There are two possible reasons why your client isn't seeing the "Save and Schedule" button in QuickBooks Online:
1. Your client is connected to the QuickBooks Bill Pay powered by Bill.com
To disconnect, try this first:
In QuickBooks Online (QBO), click the gear icon in the upper right, and choose Account and Settings
On the Account and Settings screen click the Bill Pay tab, and click Disconnect or Cancel Subscription
If unsuccessful, try these instructions from Intuit on how to disconnect.
TIP: Some accountants have reported that they don't see the "gear" icon referenced in the above FAQ, to resolve this - they had to start the setup of the Bill Pay powered by Bill.com using fake info, then on the next screen the got they "gear" icon and could successfully cancel.
2. Your client is connected to Bill.com (even if they aren't using it, they could be connected via a trial in the past)
Click here for instructions on how to disconnect.
Once Bill.com has been disconnected, the Melio "Save and schedule" button should appear.
TIP: In QuickBooks Online Accountant, if you don't see the action menu on the app that you are attempting to disconnect, you'll need to transfer the app connection to you. You'll connect the app as the accountant, this will change the app admin to you, and allow you to successfully disconnect the app. Use these instructions from Intuit on how to transfer an app connection.