Being asked to produce a piece of work inspired by something similar is not that unusual. Few businesses are truly unique and what works for one can often be appropriate to another. For a writer this is more of a challenge than you might expect - plagiarism is to be avoided like the pox, it's not only rude, but it's lazy and it's simply benefiting from someone else's hard work. The swift application of "do as you would be done by" tells you that you need to do something original.
So if you're not copying what are you doing? The best explanation I can think of is that you are taking inspiration; that's perfectly legitimate. I did a lot of that during a period of producing a series of works on the General Data Protection Regulation (GDPR) - the fundamental facts weren't disputed and the Information Commissioners Office (ICO) was the de facto source of those facts, everyone was using them. The challenge, and it is a challenge, is to package those facts appropriately, to impose a unique personality on them and to deliver that to your client's customers.
So during that period I read a lot, not only from the ICO website but other writers articles covering similar topics. I was looking for inspiration, what to do and what not to do. How were others covering this, was their approach legitimate for my clients. We all do it, especially when you're creating original content. Taking inspiration from an existing article is similar, you read to garner information, you check sources and then you sit in front of your keyboard to find words appropriate to your client, a way of telling a similar tale that is different.
Ironically I find this harder than simply creating purely original content as it comes with greater constraints and obligations. You have a duty to be mindfully original, to ensure that you are not merely coasting. If I ever feel that I am falling into the trap of mere regurgitation it's time to stop, make coffee, go away and think. It's a challenge, and at times a troublesome one but getting it right is rewarding; I will have produced something original that owes only it's genesis to another work. The words will be mine, the arrangement and emphasis will be mine and the client can be assured that when they use it, it will only reflect well on them.