Credit card details form is not working

Please help me, it's urgent and important: during the ordering process the user choose "pay with creditcard" However, no entries are possible except for the cardholder field.
When I open the CB Paid Subsruiptions settings in the backend and try to open the payment gateways, an error message appears: "Es ist ein Fehler aufgetreten! 0 Call to a member function get() on null"

What can I do?

Joomla 3? Joomla 4? Is both CB and CBSubs up to date? What payment gateway are you using? Please retest with debug mode and maximum error reporting enabled in Joomla global configuration then provide the full error callstack so we can see where the error is coming from.

My Joomla is 3.10.8
My CB is 2.7.2
My CBSubs is 4.5.3
My payment gateway is stripe

I hope you can help me. Thank you.

Stripe forms are JS driven. You most likely have a fatal JS error on your site breaking the form. Switch to default Joomla protostar template, clear Joomla cache, then retry and see if it works fine. You can check for JS errors by pressing F12 to open your browsers developer tools then clicking the Console tab while trying to go through the payment process you'll see errors in red if there are errors.

As for your file containing errors. Those are all coming from your Joomla template. Suggest contacting your template developer about the below. It's just a notice though so probably shouldn't actually break anything and your issue is likely exclusively caused by fatal JS errors, which are usually caused by the template.

Thank you for your help. I will contact the template support.

But: why I get an error in CB Subs Settings:
When I open the CB Paid Subsruiptions settings in the backend and try to open the payment gateways, an error message appears: "Es ist ein Fehler aufgetreten! 0 Call to a member function get() on null"

Where exactly are you getting that? On CBSubs > Gateways page or only after clicking to edit or create a new payment gateway? I'm not seeing such an issue in my tests. Please be sure your entire install (CB, all CB plugins, CBSubs, etc..) are up to date.