From a funtional level sponsor is the one who is responsible for providing validity to the project charter and would be the key person whose approval and signatures would be there on the project charter thereby providing "authority" to the Project Manager to assign resources

Customer is the one for whom we are building the final product and would do "product verification"

Lets take an example from an organisation hierarchy perspective ..Suppose you work as a PM in financial domain then you might get a new project the Finance vertical head with a copy of SOW and a project charter and your client is lets say "Citi bank" for which you are building a new applicaiton

Then your vertical head in your orgn or your account manager is the sponsor whereas cit bank is your customer

You can read the following article. It discusses the difference in detail.

Project Sponsor Role vs. Customer

The basic difference is that sponsor provides funding whereas csutomer provides product requriements. Secondly, for project done for profit, customer makes the payment but sponsor decides on project budget.

BR

Here is one blog i wrote on Project Sponsor and his role, you may like to make use of it.

https://www.izenbridge.com/blog/sponsor-and-his-role/

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