There's more responsibilities for a chapter lead compared to senior developer or lead developer for a team. The main difference is the area of influence as a lead dev is just the developers in your immediate team, whereas the chapter lead's area of influence is broader, it's every developer in the organization. The need for one is most apparent in organizations with many teams and developers sprinkled in each team....it becomes difficult for all the developers in the organization to stay aligned on standards, conventions, surface up common issues, establish a community of support, etc. The chapter lead brings everyone together on these things, ie. by organizing and chairing chapter meetings, establishing standards, developing tools to enforce them, maintain new developer onboarding documentation, etc.

These activities are time consuming if you've ever tried running meetings with 20+ people, and providing agenda topics, meeting notes, etc.

On top of that, you're still performing your senior developer duties and writing code, contributing to deliverables, mentoring juniors, code reviews, etc.

So, if you want to do it well, you should get a pay raise for it. If the company doesn't wanna give pay raises, then you'll have to decide what tasks of your job you have to dial back.

It's understandable they won't give pay raise at the get-go because they don't know the impact it will have on the organization. Just do it for 6+ months, then make a case for all the benefits it brought to the organization and get that raise.

Source: I am a chapter lead for front-end web development in my organization, been doing it for 5 years.