Stripe gateway sandbox, empty string error

Hello, I am testing a stripe gateway (sandbox), but I always get this error, although the country is specified.
“You passed an empty string for ‘billing_details[address][country]’. We assume empty values are an attempt to unset a parameter; however ‘billing_details[address][country]’ cannot be unset. You should remove ‘billing_details[address][country]’ from your request or supply a non-empty value.”
Although I can see the the country (here Lithuania) in the inspector:
<button type=”button” tabindex=”-1″ class=”btn dropdown-toggle btn-light” data-toggle=”dropdown” role=”combobox” aria-owns=”bs-select-1″ aria-haspopup=”listbox” aria-expanded=”false” data-id=”billingwpinv_country_605e0e049d2ba” title=”Lithuania”><div class=”filter-option”><div class=”filter-option-inner”><div class=”filter-option-inner-inner”>Lithuania</div></div> </div></button>
Can you please help me? Thanks!

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