Hello I need help I can't enter the public DMU server whenever I try an error appears I would like help to try to understand what is happening and try to solve it This problem.

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Were you using DM 1.16 (Update 65)  because that happens when load it with the 1.12 DM (Update 64)

The 1.12 server is shut down for now ( ) so play the new 1.16 one.