Hi @rubenp14,
99 out of 100 times this is the result of extra output being added to the xlsx file. This can happen due to extra spaces in front of <?php tags, or after ?> tags.
We do our best to clean up the output buffer before rendering the file; but sometimes these things still slip through.
So please checkout your functions.php and other template files to see if there are any extra characters that aren’t needed; and could cause this.
Hope this helps you out.
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