Hello,
What program have you used to generate and open the PPTX template? Please check the program you are using creates valid PPTX files to be used with phppptx.
W recommend you check and run the samples included in the package (examples folder).
For further support we'd need to check your PPTX template and the phppptx code you are running. Please note that this kind of support isn't available in the trial package. If you purchase a license, please send the PPTX you are using and the phppptx code you are running to contact[at]phpdocx.com and we'll check them.
Regards.