adding popups at checkout my app I have is getsitecontrol

I am looking for someone to help me add popups at checkout on my website, which is built on Shopify. I want to set up discount offer popups in order to increase conversions. The design should be bold and eye-catching, but not overly busy. I'd like to make sure that the popup pops up in the right way, so it won't be too intrusive, but it will get customers' attention. The discount offered by the popup should also be enticing enough to motivate customers to complete their checkout. I'm looking for an experienced developer to help me achieve this goal.