LT Digix Font Update Problem

Extetions – Templates – LTDigix – Template Options – Typography:
In the QuickStart package, when you try to click the “One click Update” button, the system displays a message: “Unexpected error occurs. Please make sure that, you have inserted Google Font API key.”

 
With a clean Joomla and clean template, when you click the “One click Update” button, the process lasts indefinitely.

However, the list of fonts is very limited.

In this case, in the directory “template\ltdigix\webfonts ” file “webfonts.json” is formed. File contents:
{
“error”: {
“errors”: [
{
“domain”: “usageLimits”,
“reason”: “keyExpired”,
“message”: “Bad Request”
}
],
“code”: 400,
“message”: “Bad Request”
}
}
 
Question: where can I install the Google Font API key?
 
Thanks in advance