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I have cloned your form and I wasn't able to replicate the problem. I visited your form (https://www.jotform.com/60362122921344) and did a test submission. I was able to submit the form and after that, the thank you page shows up.
Based on the screenshot, it seems that you trying to submit the form while you are in the Preview mode. Can you please open the actual form and try using that for a test submission?
Let us know if the issue persists. Thank you.