It seems like the error is not related to my plugin.
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<b>Notice</b>: Undefined index: cf7du_submission_id in <b>/home/nzopera/public_html/wp-content/plugins/cf7-drop-uploader/includes/cf7du_processing.php</b> on line <b>78</b><br />
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<b>Notice</b>: Undefined index: _wpcf7 in <b>/home/nzopera/public_html/wp-content/plugins/cf7-drop-uploader/includes/cf7du_processing.php</b> on line <b>84</b><br />
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<b>Fatal error</b>: Uncaught Error: Call to a member function scan_form_tags() on boolean in /home/nzopera/public_html/wp-content/plugins/cf7-drop-uploader/includes/cf7du_processing.php:86
Stack trace:
#0 /home/nzopera/public_html/wp-includes/class-wp-hook.php(287): wpcf7_posted_data_drop_uploader(Array)
#1 /home/nzopera/public_html/wp-includes/plugin.php(206): WP_Hook->apply_filters(Array, Array)
#2 /home/nzopera/public_html/wp-content/plugins/contact-form-7/includes/submission.php(285): apply_filters('wpcf7_posted_da...', Array)
#3 /home/nzopera/public_html/wp-content/plugins/contact-form-7/includes/submission.php(57): WPCF7_Submission->setup_posted_data()
#4 /home/nzopera/public_html/wp-content/plugins/contact-form-7/includes/submission.php(24): WPCF7_Submission->proceed()
#5 /home/nzopera/public_html/wp-content/plugins/contact-form-7/includes/contact-form.php(763): WPCF7_Submission::get_instance(Object(WPCF7_ContactForm), Array)
#6 /home/nzopera/public_html/wp-content/plugins/contact-form-7/includes/rest-api.php(321): WPCF7_ in <b>/home/nzopera/public_html/wp-content/plugins/cf7-drop-uploader/includes/cf7du_processing.php</b> on line <b>86</b><br />
{"code":"internal_server_error","message":"<p>There has been a critical error on your website.<\/p><p><a href=\"https:\/\/www.ads-software.com\/support\/article\/debugging-in-wordpress\/\">Learn more about debugging in WordPress.<\/a><\/p>","data":{"status":500},"additional_errors":[]}
Can you check if this is the correct name of the plugin?
“Drag and Drop Multiple File Upload – Contact Form 7”