An orchestrator function is the appropriate type of Azure Durable Function to use in this scenario, because it allows you to define the overall flow of the loan process and call other functions or activities as needed. The credit check process can be implemented as a separate activity function, which can be called by the orchestrator function and run in parallel with other actions in the loan process.
Entity functions are designed for use cases where you need to perform operations on a shared piece of state in a reliable and atomic way, such as a distributed queue or counter. In this scenario, it does not appear that there is a need to use entity functions.
There is no such thing as a "client" function in Azure Durable Functions. "Activity" functions are called by orchestrator functions to perform specific tasks, but the orchestrator function is the one that defines the overall flow of the loan process, so it is the correct answer in this case.
https://learn.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-sequence?tabs=csharp