When compiling, your app.config file is copied to the bin / Debug or bin / Release folder. If you change your app.config in the source folder but do not recompile, the change will not be propagated. You need to rebuild to move it to the folder where the code actually runs.
Alternatively, modify the bin / Debug / app.config file.
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/, (F6, Build → RebuildSolution), app.config. , , .
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