Inputted values in SignUpView won't save to backend

I am currently refactoring the signup process for a sports media app in SwiftUI and having issues trying to have it save data associated with the new user to the backend (comprised of a mix of Firebase and a custom backend) via a signup function in an AuthService class. Whenever I enter the required info to create an account (email, username, password, etc.), I get the following errors

Error: The data couldn’t be read because it is missing.
Swift.DecodingError.keyNotFound(CodingKeys(stringValue: "user", intValue: nil), Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "data", intValue: nil)], debugDescription: "No value associated with key CodingKeys(stringValue: \"user\", intValue: nil) (\"user\").", underlyingError: nil))

Here is all the relevant code:

For AuthService, the signup function is what's relevant as I call it in SignUpView and SignUp has the definition for AccountSignUp which is called in the other two files. What is not being read correctly in the data? What is missing and what can be done to fix it such that the info will be saved to the backend? All help will be greatly appreciated!

Inputted values in SignUpView won't save to backend
 
 
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