ERP
Double-entry books, stock and the work around them, next to the money that actually moved.
Two ledgers, on purpose
ERP records what is owed; Pay records what moved. Reconciled, never merged.
A period you can close
Closing freezes it, which is what makes a set of accounts something you can defend a month later.
Stock that ties out
What is on the shelf and what it is worth, in the same system as the invoice.
It is one platform, not nine subscriptions
ERP shares its customers, domains, team and bill with everything else here. Nothing is re-entered, and turning it on does not mean another login for anybody.