They want paint by numbers. What does it mean?

Everybody wants the copy-and-paste templates. They want paint by numbers. But they also want big profits. They want scalable ad campaigns that don’t quickly burn out or take tons and tons of ad rotation. Sorry, you can’t have your cake and eat it too. (Sometimes you can for a while, but it will fade, I promise.)

This is an excerpt from a book talking about Facebook Ads. I get the big idea of this passage but don't understand what "They want paint by numbers" means.

Solution 1:

Paint by Numbers is a technique for non artists to achieve a reasonable result in a painting exercise.

Each number in the painting resolves to a particular colour and the non artist just has to pick the correct colour and stay [more or less] within the lines to achieve a reasonable result.

So, in context

Everybody wants a solution [for scalable ad campaigns] that is easy and can be achieved by a non marketing expert

Solution 2:

"Paint by numbers" is a picture that is divided into regions, where each region has a number, and each number corresponds to a specific paint color; so if you are marginally competent, you end up with a correct, complete picture with little effort simply by following the rules. In particular, you need little to no skill, critical thinking, or ability to react to changing conditions or unique situations; success is all but inevitable. (The actual "Paint by Numbers" product is designed for young children with no prior painting experience.)

Along with "they want copy-and-paste templates", the passage means 'everybody wants an easy, guaranteed formula for success and profits.' (Which, if there was one, would soon stop working due to overuse.)