Type corrections

[itsme-to]

Hello, I’m submitting this pull request to fix type errors present in the package. Overall, three things have been modified:

• bool renamed to boolean in certain places.
• Added imports for the types used in the files.
• Changed the methods of the APIError class into getters to fix the conflict between error.message and error.message() that both existed.

[Majored]

Thanks, merging 👍