Before connecting your Instagram account with your Facebook page, make sure that this Instagram account is personal.
Launch the Instagram mobile app > tap the menu button > Settings > Account. If you have a Switch to Professional Account option there, you have a personal Instagram account and don't need to do anything.
If you see Switch to Personal Account and Switch to Creator Account options in this menu, then you have a Professional account and need to switch to a Personal account.
Your personal Instagram account is automatically converted to the Instagram Business account when connecting your Instagram account with your Facebook page. You just need to add information about your business.