Could you please clarify the error like why it is displaying should not have additional properties instead of mismatch in properties

This is just the way the errors are presented. It uses the language of OAS and JSON schema, which is the underlying comparison technology used, and should allow better googling etc. Additional properties are a really key concept in JSON schema, but also very complicated. Basically, it means you are requesting additional properties in the pact file - i.e. json fields - that aren’t present in the schema (OAS)