OnePlus
Add a Second Account auf OnePlus
OnePlus links exactly one Google Account to your phone during the initial setup. Every other account, whether it is a second Gmail address, a work Exchange login, or an Outlook mailbox, has to be added manually before it can sync contacts, mail, or calendar entries.
Accounts tied to a specific app, such as Facebook or WhatsApp, are not part of this list. Those log in inside their own app and store data locally or through their own servers, so they never appear under system accounts.
To register a new account, open the Settings, then tap on Accounts. Tap on Add account and pick the account type you need from the list, then follow the instructions on screen to sign in.
Once the account is added, the phone starts syncing contacts, mail, and calendar in the background, depending on which sync toggles you leave active for that account. If sync stops working later, check that the account still shows up under Accounts and that its toggles are switched on.

