I've added A footer message on invoices and sales receipts but it doesn't print or appear when send to to client . please help

You may have used a different template or the modern one, which is why the footer message you've added didn't print or appear when sending invoices, ligia1.

When creating invoices and sales receipts, make sure to select the correct or preferred template to ensure all your personalized details are displayed and printed correctly. To do this, here's how:

1. Open a new or existing invoice or sales receipt.
2. For the invoice, go to the Manage tab and select the Design section to choose the appropriate template.
3. On the Sales Receipt page, choose the Customize option to pick the right template.
4. Once all information is entered, click Print or download or Print or preview to view the details of the sales forms and then send them to your respective customers. 

For more insight about personalizing sales forms, please see this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Additionally, record customer payments as soon as invoices are paid. This keeps your accounts balanced and maintains accurate bookkeeping.

Please let us know in the comments if there's anything else you need help with in customizing your sales transactions. We'd be glad to assist you further.