Please help us help you and fill where relevant:
LimeSurvey version: 6.10.2
Own server or LimeSurvey Cloud: LimeSurvey Cloud
Survey theme/template: fruity_twentythree
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Hello,

I created a survey using the free plan of limesurvey.net and I get the following error on any page of my survey: Did not saveAn unexpected error has occurred and your responses cannot be saved.Your responses have not been lost and have been emailed to the survey administrator and will be entered into our database at a later point.

I tried to export the survey and import it into a new one, but I still get the same error.
You can visualize and try out the survey here: inkuele.limesurvey.net/434975?newtest=Y&lang=en

Any idea on what the problem could be?

www.limesurvey.org/support/contact-corporate

This seems to be an issue with the server you are on. I don't see that with other LS instalaltions.

We here in the forum are users that help users and have no insights on the servers of Limesurvey GmbH.

In your case, please open a support ticket with the Limesurvey GmbH. One issue with that could be the fact that you are on a free plan. Not sure if they provide support for that.