Below you find my Mailchimp amp-form. When I enter data and submit the form, the data is being transferred to Mailchimp but I am getting my amp-mustache error instead of the success message. What did I miss out? Thanks for an idea how to fix the error. Take care and Happy Easter!

Errors in the console are:

Access to fetch at 'https://ingereck.us15.list-manage.com/su&bscribe/......__amp_source_origin=https%3A%2F%2Fingereck.net' from origin 'https://ingereck.net' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

POST https://ingereck.us15.list-manage.com/subscribe/ ... __amp_source_origin=https%3A%2F%2Fingereck.net net::ERR_FAILED

[amp-form] Form submission failed: Error: XHR Failed fetching (https://ingereck.us15.list-manage.com/...): Failed to fetch​​​
    at ab (https://cdn.ampproject.org/v0.js:28:169)
    at Xa.f.createExpectedError (https://cdn.ampproject.org/v0.js:23:343)
    at https://cdn.ampproject.org/v0.js:143:154

My server’s (NGINX) CORS headers are:

add_header Access-Control-Expose-Headers "AMP-Access-Control-Allow-Source-Origin";
add_header Access-Control-Allow-Headers "Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token";
add_header Access-Control-Allow-Credentials "true";
add_header Access-Control-Allow-Origin "https://ingereck.net/";
add_header Access-Control-Allow-Methods "POST, GET, OPTIONS";

This is the form:

<div class="subscribe-card-container">
    <div class="subscribe-card">
        <form method="post" class="main-form" action-xhr="https://ingereck.us15.list-manage.com/subscribe/post-json?u=MYUSERID&id=MYLISTID&c=?&" target="_top">
<div class="indicates-required"><span class="asterisk">*</span> denotes a mandatory field
    </div><p></p>
<label for="form-email">Email Address <span class="asterisk">*</span></label>
            <div class="input">
                <input type="email" name="EMAIL" id="form-email" required="">
            </div><p></p>                
<label for="form-fname">First Name</label>
            <div class="input">
                <input type="text" name="FNAME" id="form-fname">
            </div><p></p>
            <label for="form-lname">Last Name</label>
                <div class="input">
                <input type="text" name="LNAME" id="form-lname">
            </div><p></p>
<!-- real people should not fill this in and expect good things - do not remove this or risk form bot signups-->
    <div style="position: absolute; left: -5000px;" aria-hidden="true"><input type="text" name="b_MYUSERID_MYLISTID" tabindex="-1" value="">
			</div>
            <input type="submit" value="Subscribe" class="btn">
            <div submit-success="">
                <template type="amp-mustache">
                    <p class="form-submit-response">
                        Thank you for subscribing {{FNAME}}!<br>
You are almost there! To complete the subscription process, please click the link in the email we just sent to you.
                    </p>
                </template>
            </div>
            <div submit-error="">
                <template type="amp-mustache">
                    <p class="form-submit-response">
                        Ooops! Sorry, there was an error.
                    </p>
                </template>
            </div>
        </form>
    </div>
</div>

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