Prometheus OR when using rate()
| is for regular expressions, PromQL doesn't have a | operator (but it does have an or operator). You need to specify that the matcher is a regex rather than an exact match with =~:
rate(application_httprequest_transactions_count{env="test",app="MyApp",server=~"myapp-test-58d94bf78d-l9tdv|myapp-test-58d94bf78d-jdq78"}[15m])*60