Hey Federica,

You can add the script in the template file for the invoice thank you page.
You can find the file here : root\components\com_payplans\themes\wireframe\thanks\default\default.php

Do the changes using template overriding so changes will not be lost on upgrade.
See here : https://stackideas.com/docs/payplans/administrators/customization/template-override

Let me know if you have any queries.

Hello,
I created a copy of file here:
[...]/templates/yoo_chester/html/com_payplans/themes/wireframe/thanks/default/default.php
can you confirm me if "com_payplans/themes/wireframe/thanks/default/default.php" path is correct to override this file?

If yes is not working:
Example: https://www.mantrayogacentre.com/piani-tariffari-disponibili/thanks/8o56wjcm6247.html

Thanks

Hey,

can you confirm me if the "com_payplans/themes/wireframe/thanks/default/default.php" path is correct to override this file?

The overridden path should be as shown below.
[/templates/yoo_chester/html/com_payplans/thanks/default/default.php

You can refer template overriding document for more details.
See here: https://stackideas.com/docs/payplans/administrators/customization/template-override

Update us if the still issue persists.