Suggestions

1. There could be an “Invite a Friend” option.

2. Instead of entering recycled waste inputs by grams, we could find a simpler way for users.
   For example, they could select “1 plastic bottle”, and the app could handle the gram calculation internally.

3. Users could be asked to share photos to verify their inputs.

   My comment: This might not be very practical, since we can’t be sure if the uploaded photos are genuine.
   So there may not be much we can do about this.

4. Users could be informed about the locations of recycling centers, especially for electronic waste.
   If necessary, similar information can also be provided for other waste types.

5. In the Tips section, different methods can be used to motivate users to recycle.
   It could also remind them that recycling can have financial benefits.

6. If the CO2 emission value is going to remain, we can calculate it ourselves using reasonable coefficients instead of relying on an API.

7. If users join multiple challenges — for example, recycling plastic waste — their progress might automatically increase in more than one challenge.
   A control mechanism should be created for this so that each challenge is evaluated separately.

8. If a user enters an unusually large amount of waste, there should be a verification mechanism that warns the user and asks for proof.
   They might have entered it by mistake, so a warning would make sense.

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Notes (as a reminder)

1. Dark mode will be added.
2. Multi-language support will be included.
3. Text size will be adjustable in Settings.
4. A show/hide password feature can be added to the Sign Up and Sign In pages.