Hey there, welcome to the Streamlit community and thanks for reaching out! 
Sorry you’re hitting a 403 error on your very first deploy—this is a common issue for new users and usually means your account was mistakenly flagged by Streamlit Community Cloud’s automated protections (often for exceeding fair-use limits, even if you haven’t deployed before).
To resolve this, you’ll need to open a support ticket and include your GitHub username. The Streamlit team will review your case and help unblock your account. You can find the step-by-step process in the official docs: How to submit a support case for Streamlit Community Cloud. For more details, see the FAQ: Login attempt to Streamlit Community Cloud fails with error 403. Community members, feel free to jump in if you’ve experienced this and have tips to share!
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