If you have problems with activate license, you should use to reactivate old burploader (for older versions like 2.1.07). Run:
java -jar burploader-old.jar
Activate burp license manually with burploader-old.jar:
copy license request from loaded burpsuite_pro_v2021.5.jar to burploader-old, copy license response and paste to BurpSuite, press next. Done.
P.S.: There we use the same loader as in 2020.4 version (https://github.com/x-Ai/BurpSuiteLoader).
P.P.S.: burp/StartBurp has been compiled by a new version of the Java Runtime (class file version 53.0).
You should use java9+ava Runtime (class file version 53.0).
You should use java9+/BurpSuiteLoader).
P.P.S.: burp/StartBurp has been compiled by a new version of the Java Runtime (class file version 53.0).
You should use java9+
```lass file version 53.0).
You should use java9+se java9+