Prevent service request from being closed if it has a pending approval

Prevent service request from being closed if it has a pending approval

We are using SDP  11205. We have created some service request templates which have a single stage approval set up in the workflow. However, we have found the request can be closed without the approval being approved (regardless if approval status it "to be sent" or "pending approval"). How can we prevent a service request from being closed if it has a pending approval? Thanks.
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