The error NO X11 DISPLAY means that for some reason isCOBOL try to access AWT/SWING GUI Interface and your system have not that.
If your cobol program have not any GUI interface included, you can try to set the java.awt.headless=true property on your run command:
iscrun -J-Djava.awt.headless=true .....
or
java -Djava.awt.headless=true .....

If your cobol program include some textual ACCEPT/DISPLAY you need to turn on isCOBOL CHARVA support adding -t option:
iscrun -J-Djava.awt.headless=true -t ....
or using the property
iscobol.guifactory.class=com.iscobol.gui.client.charva.GuiFactoryImpl with java:
java -Djava.awt.headless=true - Discobol.guifactory.class=com.iscobol.gui.client.charva.GuiFactoryImpl

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