Add data with Separate Form toi Collection Restaurants

[MarGer1962]

Hi,
I have this question.
I have a separate HTML file which contains a form.
Then - if the form is filled in and you click on submit - the data should be sent to the the firestore > restaurants collection.

I have a copy of the form included.
HTML-Form code.txt
I do not understand why i can't get it to work.
Can some one help me out? (maybe to give me a link to a tutorial about this?or a publication?)

Thanks in advance