uploading a specific file type not possible

Hi, on a clients website it has to be possible to upload .stl files. I’m using WordPress 4.8.1, Caldera Forms 1.5.5 and the theme is Avada 5.2.1

I put the following code into the themes function.php:

function my_upload_mimes() {
$mime_types = array(
’stl‘ => ?application/octet-stream‘,
);
return $mime_types;
}
add_filter( ?upload_mimes‘, ?my_upload_mimes‘ );

I also customized the php.ini on the server and added the additional mime type I need.

Now I can upload .stl files in the media library in the backend, but not with my Caldera form: I’m always getting the following error: “This file type is not allowed. Please try another.”

The form ist correct configured, .stl files are allowed. I also tried any and all of the mime type plugins and last but not least I tried it with putting the snippet ?define (‘ALLOW_UNFILTERED_UPLOADS’, true);“ in my wp-config.php – but unfortunately nothing worked.

Could you please give me advice how to solve this issue?

Thanks a lot!

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