Hi Jean Loup,
I just checked your booking form and I'm getting this message:
You must enable Billing on the Google Cloud Project associated to this client ID, at https://console.cloud.google.com/project/_/billing/enable.Learn more at https://developers.google.com/maps/premium/new-plan-migration
This means that you haven't enabled Billing in your Google console by adding a valid credit or debit card.
Google gives you $200 of credit to use Google Maps API every month so it's highly unlikely that you go over this limit, however, you must enable Billing or the API keys will not work.
When you enable Billing correctly everything should work as expected.
Hope this helps.
Kind regards.
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