UPD: my case was resolved with the help of support. I managed to contact them in chat. The issue was that my account was relatively new - few months, and not everything was verified. Support representative gave me a call and verified my phone number, email, gave instructions how to verify the card (in fact I wasn't adding a card, since I was only using a bank account, but still they advised to add a card and verify it to make sure my account is verified in everything). After everything was verified, in about 48 hours I was able to send the invoices again. Maybe that is useful for someone. good luck!
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