We generally do weekly or bi-weekly demos with the client.
We use these as clear opportunities to show progress and get feedback on the work we have done for the client. Some clients like to be in the nitty gritty and get regular builds of the apps and provide feedback along the way. Others even when we provided regular builds won't really look at them until we have a demo. We do demos irrespective of the clients behavior as it is good practice to take a step back and look at the work that has been done and how it relates to the higher level product goals.
When we do our Planning & Prioritization meeting each week we discuss our plans for what we are going to demo the next week. We are extremely careful not to let things be driven completely by the demo and become DDD (Demo Driven Development). But it is an important attribute to take into consider while planning and prioritizing work.
We generally try and avoid demos of APIs and network requests as much as possible and focus on demos of application UI as much as possible. There are of course exceptions to this. For example if the project was to build a public facing API for a service. Then it would make sense for the demo to be Paw/Postman interacting with the public API.