The Request ID is a unique on-chain and off-chain identifier genrated at runtime for a request.
On-chain, Midpoint maintains the uniqueness of this rolling ID by incrementing the on-chain Request ID for each request. This Request ID is returned to the contract that initiated the midpoint request. This is done inside Startpoints, and each chain generates a Request ID that is unique to its chain.
Off-chain, Midpoint assigns a unique rolling ID for each request that is generated.
Request IDs allow serialization of requests as they move off-chain and then back on-chain. By posting the request ID back on-chain, you can tie a response to a particular request.