You control the Shopify option "Continue selling when out of stock" directly from PlentyONE. The setting "Stock restriction" on the respective variant in PlentyONE is responsible for this.

This is how the assignment works:

• If you want to ALLOW selling at zero stock (overselling ON):
  • Select the stock restriction "None" or "Do not maintain stock balance for this variant" in PlentyONE.
• If you want to STOP selling at zero stock (overselling OFF):
  • Select the stock restriction "Based on net stock" (net stock level) in PlentyONE.