Check the supplier interface first
Start with the EPOS supplier, installed version and account capabilities. Confirm whether stock and product data are available through a supported API, export or connector, and whether online orders can be written back.
Do not assume a named retail system supports every required operation. Access costs, supplier approval, update limits and test environments are discovery questions that affect the scope.
Agree what stock means
On-hand quantity, reserved stock and stock available to sell can differ. Decide which quantity the website should use and what happens when a shop sale and an online order compete for the same item.
Use stable product and variant identifiers. A barcode can help link records, but the relationship must be checked against the actual catalogue, especially where packaging, variants or supplier codes differ.
Build a reconciliation route
If a stock update fails, the team needs to know which product is affected and which system holds the authoritative value. Decide whether sales pause, a conservative availability rule applies or staff review the exception.
Test simultaneous sales, cancelled orders, returns and repeated notifications. Ask for clear logs and a safe reconciliation process so a background integration does not silently overwrite a discrepancy.