Thanks for coming to the Community for your concern. There could be a possibility that you might have logged in to a different account. I'm here to guide you to ensure you can see all your data on the app.
First off, log out to your app, then log back in using the same credential as you logged in to the web. You should be able to see all your customers' and suppliers' contacts.
If you're having trouble logging in, click the I forgot my user ID or Password link to recover your credentials. Then, follow these steps below:
Enter your phone number or email address in the field box, then click Continue.
Choose an option to reset your login information: Get a code emailed to or Recover my account a different way.
Click Continue. If you used your email address to verify the account, you’ll receive an email with your user ID.
For password reset, you can follow the same steps above. Then, you'll receive an email with a password reset link.