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The invoicer on an account cannot be changed once an invoice exists on that account UNLESS the following conditions are met first:
All invoices are closed
All balances and account are zero (by way of adjusting transactions or otherwise)
All payments and credits are marked as 'Disbursed'. If they cannot be disbursed they must be reversed on that account
Invoicers must be setup before any billing takes place
Parent accounts must be active for sub-accounts to invoice
EngageIP 8.6.0+: Accounts must be in the same bill group as their invoicer and usage invoicer
EngageIP 8.6.0+: Invoicer options on an account will be greyed out (read-only) if the account's owner is setup to receive invoices. Specifically, if the owner is configured with a ‘Owner Parent Account Billing Type’ > ‘Bill Owner…/Bill Branded Owner…’ option. See the Configuring Branded and Unbranded Owners article for more information on configuring owners
EngageIP 8.6.0+: An account's bill day must be in sync with the bill day of the account's invoicer
EngageIP 8.6.0+: Changing the bill day of an account setup as an invoicer will update the bill day of all accounts configured to use that invoicer (via an EngageIP job)
EngageIP 8.6.0+: A sub-account cannot be the usage invoicer for its parent account
EngageIP 8.6.0+: An account setup as a usage invoicer (i.e. invoiced for usage generated by other accounts) must be configured to be its own invoicer and usage invoicer
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