Error please try again on 1st submission, 2nd submission successful?

Whenever I submit the application the first time, it gives me this error with a YELLOW border:
One or more fields have an error. Please check and try again.

Then on second submission, I get this with green border:
Thank you for your message. It has been sent.

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On second attempt just clicking the submission button twice, no other changes, it works.

Please help me fix. I tried everything.

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