Rest API Create customer Error HTTP 500

[Franz Fuchsbauer]

I try to create a customer like it is described in the docs. But I receive an HTTP 500 with an Internal Server error.
Any idea?
Reading the customer with a GET https://MYDOMAIN.atlassian.net/rest/servicedeskapi/servicedesk/1/customer
is possible.

POST https://MYSUBDOMAIN.atlassian.net/rest/servicedeskapi/customer
Authorization: Basic MYBASICAUTH
Content-type: application/json
X-ExperimentalApi: opt-in

{
    "email": "fred@example.com",
    "fullName": "Fred F. User"
}

-------------- RESPONSE --------------
Transfer-Encoding: chunked
HTTP/1.1 500 Internal Server Error
x-envoy-upstream-service-time: 15102
Server: AtlassianProxy/1.19.3.1
ATL-TraceId: 3de2e070ba5b744a
X-Content-Type-Options: nosniff
Connection: close
Date: Wed, 15 Dec 2021 15:38:43 GMT
set-cookie: atlassian.xsrf.token=b4bcb7ec-47b1-463b-97b3-b80e47b338b8_9ace808d378704d6b972a3afbee5ceed1575f1d1_lin; path=/; SameSite=None; Secure
Strict-Transport-Security: max-age=315360000; includeSubDomains; preload
x-arequestid: 6e1dc955-0ba7-4326-9c26-ea4e175095e4
x-aaccountid: 61b5d0d6ef5b460071ea97cf
timing-allow-origin: *
X-XSS-Protection: 1; mode=block
cache-control: no-cache, no-store, no-transform
Expect-CT: report-uri="https://web-security-reports.services.atlassian.com/expect-ct-report/global-proxy", enforce, max-age=86400
Content-Type: application/json;charset=UTF-8

{
  "errorMessages": [
    "Internal server error"
  ],
  "errors": {}
}

[Franz Fuchsbauer]

Today it works again.