Your 'Primary Account' is the account either used by you, or chosen by you, to make deposits and withdrawals to / from your Marygold account. Your Primary Account is the only external account you may use to make deposits (although you can change your Primary Account).
For new customers, when you make your first deposit we assume that the paying account is the external account you wish to be your Primary Account (unless you have already linked an external account, and nominated that account).
Once your initial deposit is received, the paying account will be automatically set to be your Primary Account, and from that moment on all deposits and withdrawals will need to go through this external account.
Although it is possible to also 'link' your Primary Account to the Marygold app (for example if you want to create pay day nudges based on this external account), this is not a requirement and does not happen automatically. If you want to link your Primary Account, then you must do this proactively.