It's a tricky one - and it depends very much on your sector of work.
For example, if you are going from a small-ish IT provider to a larger Corporate IT Environment - then when the Interviewer asks about why you can't get growth opportunities at your current position - you could answer that the size of the company and their target market limits the exposure you can get to certain technologies and solutions at scale.
Some companies also don't have much opportunity for advancement past a certain point (For example, it might be the Owner and their Children that occupy all the top spots)
All of these are perfectly acceptable retorts to when you are challenged on this point.
However - all of this, I feel is beating around the bush - you've indicated that you are changing jobs because you want more $$$ which is perfectly acceptable.
So, you could go with the honest truth "My current employer doesn't have the budget for a market-rate salary" but people tend to get squeamish about this.
Which is where we get into the realm of 'Stock answers to Stock questions'
"I want new challenges"
"Growth opportunity"
"Looking for better Work/Life balance"
You know - any of the generic answers - what matters IMO is how you follow it up, what context you add.
So for example - I'm a Microsoft Man, I've got a few Azure certs, if my company decided that it was going to go fully into AWS, I might use this as a reason:
"My interest and skillset is in MS Azure and I want to develop it further, however my current employer has indicated a preference for AWS, which I'm not as enthused at learning. I understand this opportunity is primarily for an Azure Administrator, which is why I applied"
I've taken that from a 'Stock Answer' to an answer that gives the interviewer an insight into what actually drives me (without saying 'Mo Money')
Putting all of this together - It's a bit of a stock answer, but if you take a couple of moments to add some additional context (and it helps if you do it without prompting) then it takes it from a 'meh' answer, to a good answer.
e.g. "The main reason is I'm looking for Growth opportunities. My current employer does XYZ and that means I'm limited to ABC - and I want to be getting exposure to PDQ"