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I cloned your form to test the Facebook embed and it appears to be working fine on my end:
Usually a 500 error indicates an internal server error or a general issue with connecting to the server. My recommendation would be to clear your web browsers cache and history, then try the integration once again. If this still does not work, I would recommend trying a different web browser other than internet explorer. Google Chrome tends to work the best with our form. If this also does not work, let us know and we will be happy to look into this further.
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