Update src/pages/monetization/billing-api/index.mdx

Co-authored-by: oliwiapolec <[email protected]>

Author: olek-p

src/pages/monetization/billing-api/index.mdx

@@ -275,7 +275,7 @@ There are three possible recurrent charge flows:
 - `pending` -> `accepted` -> `processed` -> `active` -> `frozen`
 - `pending` -> `declined`
 
-Additionally, whenever payment is due and an invoice is issued, the charge enters the `past_due` status. As soon as the invoice is paid the status changes back to `active`.
+Additionally, whenever a payment is due, and an invoice is issued, the charge enters the `past_due` status. As soon as the invoice is paid the status changes back to `active`.
 In the best-case scenario, this only takes a few seconds. In other cases, the `past_due` status may be used to, for example, display a pending invoice notification to the app user or limit the app's functionality.
 
 <Section>