Processing form ends with Internal Server Error

Hey there, I’m using the plugin for a good while now. Haven’t had bigger issues so far. Now, whatsoever, a submitting form results in this error message and the form doesn’t get send via mail. When Generate PDF is deactivated Contact Form 7 sends the mail again as usual.
Using version 5.8.2 of Contact Form 7, WordPress 6.4.1 and PHP 8.1.

Response { type: "basic", url: "wp-json/contact-form-7/v1/contact-forms/459520/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", … }

<entries>

<prototype>: HeadersPrototype { append: append(), delete: delete(), get: get(), … }

ok: false

redirected: false

status: 500

statusText: "Internal Server Error"

type: "basic"

url: "wp-json/contact-form-7/v1/contact-forms/459520/feedback"

<prototype>: ResponsePrototype { clone: clone(), arrayBuffer: arrayBuffer(), blob: blob(), … }
index.js:1:7071

Can’t make much out of this response. Do you have any advise, what might cause this error?
Thanks in advance!