Contact Form 7 + Double Opt-In: Submit results in an error (error 500)

Hi dear,

When i press the Submit-Button in Contact Form 7, i get the error shown below. An Opt-In-E-Mail is not sent. The error appears after exceeding a certain Number of form fields (a little over 50). If I disable the plugin Double Opt-In, it also works with more form fields.

I use contact form 7 Version 5.7.2 and Double Opt-In Version 2.12.

Thanks to everyone who can help me. Regards!

Response { type: "basic", url: "https://siebenpfeiffer-gymnasium.de/wp-json/contact-form-7/v1/contact-forms/1312/feedback", redirected: false, status: 500, ok: false, statusText: "Internal Server Error", headers: Headers(12), body: ReadableStream, bodyUsed: false }
?
body: ReadableStream { locked: false }
bodyUsed: false
headers: Headers(12) { "access-control-allow-headers" → "Authorization, X-WP-Nonce, Content-Disposition, Content-MD5, Content-Type", "access-control-expose-headers" → "X-WP-Total, X-WP-TotalPages, Link", "cache-control" → "no-cache, must-revalidate, max-age=0", … }

ok: false
redirected: false
status: 500
statusText: "Internal Server Error"
type: "basic"
url: "https://siebenpfeiffer-gymnasium.de/wp-json/contact-form-7/v1/contact-forms/1312/feedback"
<prototype>: ResponsePrototype { clone: clone(), arrayBuffer: arrayBuffer(), blob: blob(), … }index.js:1:6781
    l https://siebenpfeiffer-gymnasium.de/wp-content/plugins/contact-form-7/includes/js/index.js?ver=5.7.2:1
    (Async: promise callback)
    l https://siebenpfeiffer-gymnasium.de/wp-content/plugins/contact-form-7/includes/js/index.js?ver=5.7.2:1
    m https://siebenpfeiffer-gymnasium.de/wp-content/plugins/contact-form-7/includes/js/index.js?ver=5.7.2:1

    (Async: EventListener.handleEvent)
    m https://siebenpfeiffer-gymnasium.de/wp-content/plugins/contact-form-7/includes/js/index.js?ver=5.7.2:1
    <anonym> https://siebenpfeiffer-gymnasium.de/wp-content/plugins/contact-form-7/includes/js/index.js?ver=5.7.2:1
    <anonym> https://siebenpfeiffer-gymnasium.de/wp-content/plugins/contact-form-7/includes/js/index.js?ver=5.7.2:1
..

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