A good review campaign is designed to avoid biased responses. So: don't pay for good reviews, pay for all reviews. Even better if it's paid up front, so the reviewer doesn't feel any pressure to go in a certain direction.
I've done several reviews, and I usually mention the bad stuff. There's no point in mentioning the good stuff, so I mention what I think can be improved. I've had positive responses to this approach.
But what you did was not a review, it was feedback from the service. They are different things.
The revision must be given spontaneously by the client, without being asked.
Feedback is requested directly from customers, to find out where to improve and how the service is working from the user's point of view.
What’s customer feedback?
Customer feedback is solicited feedback which often comes in the form of surveys. These can be requested via email (for example, an order confirmation email), website, social media, over the phone, and more. Essentially, customer feedback is a customer’s opinion gained after an organisation has asked for it. This can be concerning a product or service and can be requested at different stages in the customer journey. It’s internal, with only the organisation seeing that feedback.
What’s a review?
Reviews are typically non-solicited feedback gathered on an open, third-party platform where anyone can share their thoughts, positive or negative. Commonly, the business being reviewed cannot filter or delete negative reviews. The only action they can take is to respond and attempt to rectify the situation.
If the campaign is for feedback, it makes sense. But not a campaign for review. This in my opinion.
. I hope it was real 
