Hi Mihaly, Slobodan, and Cristache,
This is a known issue and the team is working to resolve it. I've forwarded to your account information to the Customer Support Team so that they can reach out to each one of you with more information, and send you updates through an email support ticket.
EDIT TO ADD: Hi Mihaly, the team has confirmed that you were able to send out a proposal recently. Let us know if the issue persists.
Please know that this is a known issue, and the team is investigating it further so that it can be resolved. I have forwarded your account information to the Customer Support Team and they will get in touch with you separately for more information and updates about the issue.