Timuriy on "[Plugin: Affiliates Contact Form 7 Integration] 500 Internal Server Error while submit Contact Form 7"

Good day!
I have integrated Affliate with my Contact Form 7(v. 3.8.1), and since then I'm getting "500 Internal Server Error" while submitting Contact Form 7.
What could cause this error?

https://wordpress.org/plugins/affiliates-contact-form-7/