Can you send the base64 encoded payload over (strip any key information)? I can test it out. We don’t have special character restrictions so this may be just a coincidence and something else may be driving this issue.  

This has also been a plague for us. We strip out any non-ASCII characters before sending to Klaviyo. This solved a lot of issues for us but we still see requests fail for what I’m assuming are character restrictions we don’t know about.

Hi @cdetdi & @Anthony Smith,

Thank you for sharing this information with our Klaviyo Community. And thank you @andrew.smith for your input.

Our Track API does not have any restrictions on any type of unicode/special characters. 

I have outlined some solutions if you encounter a rejected track request in the post linked below which was asked earlier by @Anthony Smith, I hope this helps clear up the issue.

Thanks and have a great day.

@andrew.smith we rewrote our integration fully so that the calls are all built first as php arrays and then use json_encode to build the JSON.  That has solved most of the special character issues.  Even simple calls which we originally had manually authored the JSON now go through that process.  
 

we still have a few random errors which we are working with CS to solve