After starting a sync nothing happens, just blank result

Like said via mail: not enough info, you’d need at least to check the apache logfiles for info.
If it doesn’t work for you, also check your php version (facebook requirements …).
And for older versions (not supported):
https://www.ads-software.com/plugins/eme-sync-facebook-events/developers/

This is the php-error

Fatal error: Call to a member function format() on null in /hsphere/local/home/mlhemtech/skaneplus.se/wp-content/plugins/eme-sync-facebook-events/eme-sync-facebook-events.php on line 475

Ok, that means it is an access token without expiration. And yes, it seems I haven’t taken that into account … yet.
This fix should help here:
https://plugins.trac.www.ads-software.com/changeset/1602763/

Updated to 1.0.26 and now a new fatal error:

Fatal error: Uncaught exception ‘Facebook\Exceptions\FacebookSDKException’ with message ‘Signed request has an invalid signature.’ in /hsphere/local/home/mlhemtech/skaneplus.se/wp-content/plugins/eme-sync-facebook-events/Facebook/facebook-php-sdk-v5.0.0/SignedRequest.php:281 Stack trace: #0 /hsphere/local/home/mlhemtech/skaneplus.se/wp-content/plugins/eme-sync-facebook-events/Facebook/facebook-php-sdk-v5.0.0/SignedRequest.php(156): Facebook\SignedRequest->validateSignature(‘)\x80\xF4pz\x999\xFEb\x9D\x85\x9D,\x8E\x14…’, ‘e\n\xF7\xD7\xBFd0]\xDB\xDB\x8C\xB1\xCBh<…’) #1 /hsphere/local/home/mlhemtech/skaneplus.se/wp-content/plugins/eme-sync-facebook-events/Facebook/facebook-php-sdk-v5.0.0/SignedRequest.php(66): Facebook\SignedRequest->parse() #2 /hsphere/local/home/mlhemtech/skaneplus.se/wp-content/plugins/eme-sync-facebook-events/Facebook/facebook-php-sdk-v5.0.0/Helpers/FacebookSignedRequestFromInputHelper.php(84): Facebook\SignedRequest->__construct(Object(Facebook\FacebookApp), ‘ZQr3179kMF3b24y…’) #3 /hsphere/local/ho in /hsphere/local/home/mlhemtech/skaneplus.se/wp-content/plugins/eme-sync-facebook-events/Facebook/facebook-php-sdk-v5.0.0/SignedRequest.php on line 281

By default I now use 2.8 for the facebook API, maybe your app doesn’t like that.
See this url for other people that had similar issues with facebook:
https://stackoverflow.com/questions/23566644/integrating-facebook-in-php-giving-invalid-signed-request-with-oauth-data

Btw: also check your app settings on facebook and check your app id and secret.

Ok, creating a new facebook app solved problem with fatal error. But you should consider adding some error handling telling the user what failed.

Thanks for your help!