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Could you please provide us more details of the problem you are having?
I do not have a Mac computer to test it fully, but I have a simulator that I used to view your form and was able to submit without any problems. Here's a screencast of it:
I'm testing your website using a Mac OS X Yosemite 10.10.5. If you are getting any error messages, please do let us know, a screenshot would also help us a lot. Here's a guide on how to take a screenshot on Mac: https://support.apple.com/en-ph/HT201361
You could also try using a different browser like Chrome and see if the problem persists.
We'll wait for your response.