Hi there, neto1.

Thanks for taking the time to reach out to us. Allow me to address your concern, so let me get this straightened out. 

As of now, QuickBooks Online doesn't have any feature to sent a notification through text once the customer made a payment for their invoice. I can see how this feature would be helpful for you, I'd recommend sending feedback directly to our product developers for future updates. 

Here's how you can send feedback: 

1. Click the Gear Icon.
2. Select Feedback. 
3. Click Next and choose Feedback under Category option.
4. Select Save. 

For future reference, you can visit this article: How to record a customer payment. 

Please know that you're always welcome to post if you have any other questions. We're always here to help you out.