4xx should employ a standardized schema as part of the response, ideally something like Problem Details for HTTP APIs, expressed as OpenAPI and JSON Schema. 4xx should provide API consumers with what they need to know to fix their requests and try again in a consistent way across all types of APIs.
Problem Details for HTTP APIs and HTTP 4xx series provides a standardized base for communicating problems encountered by API consumers, which should be the same across all HTTP APIs. While the challenges encountered by your user may be unique to your API resources and capabilities, expressing the semantics of problems encountered via HTTP will be the same.