php export xls, error: file format and extension mismatch. The file may be damaged or unsafe. Unless you trust the source, do not open it.

Open the file given as follows

Add the following code in the header

1 ob_end_clean();
2 header('Content-Type:application/vnd.ms-excel');
3 header('Cache-Control: max-age=0');

as follows:

 

 

Reference: https://www.cnblogs.com/jthb/archive/2013/05/24/3097485.html

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