Singular:
Sorry, there is insufficient stock to fulfill your order with respect to the tickets you selected in relation to this event: %s Sorry, there is insufficient stock to fulfill your order with respect to the tickets you selected in relation to this event: %s

Plural:
Sorry, there is insufficient stock to fulfill your order with respect to the tickets you selected in relation to these events: %s Sorry, there is insufficient stock to fulfill your order with respect to the tickets you selected in relation to these events: %s

This plural form is used for numbers like: 1, 21, 31

This plural form is used for numbers like: 0, 2, 3