White page when I sent newsletters

HI,

I’ve configured mailpress but i’m not an expert,

i ve installed the add-ons ” Connection PHP” to send newsletter, i m sure if it’s the good one for what i need.
The thing is when i send it, i have automatically a white page but my newsletter is gone and i received it.
i’m sure there is a confirmation page, no ?

i’d like to send 20 000 by month what do you suggest me ?
i really need help.

Thanks

i’m using mailpress 5.4

https://www.ads-software.com/plugins/mailpress/