Internal server error when prestashop generates voucher codes

hello , i've installed the presta module on our presta 1.7.4.2 , when we go to generate vouchers it keeps going on error 500 , after minutes of wait . the php versione is 7.1.20 mysql versione 5.5.57 the prestashop debugger don't say anything , neither the csv file has been generate . The php process as been raised to 3000 seconds timeout to try to debug it , bt nothing 

Error 500 when shop generates vouchers

Hello

- When you try to generate several vouchers (for example 5 vouchers only) everything works as expected?

- Most common problem is related to fact that voucher settings were not saved: 

So, before you will git button to "generate" vouchers, please make sure that you saved the settings of coupons that module will use to generate vouchers.