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Do you use Mozilla? Try to send by via Chrome or Opera. I don't know why it doesn't work via Mozilla...

I used Chrome and notice a warning to load unsafe scripts. I tried to load unsafe scripts but unable to send.

To resolve I think copying all website files to local https server and change all references in webpage code from http to https. For example jquery.validate.js is referenced through http instead of https. Here is related issue: https://stackoverflow.com/questions/3562358/can-i-use-jquery-form-js-in-an-https-page

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You are really expert in security things! I couldn't realize about this unsafe scripts. Thanks for solution!

So I fixed it. Try to send again.

It works for me with Chrome and Brave browsers now, I haven't tested Firefox or others.

I am happy that it works fine!