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The EAS stack does not currently support TLS 1.2 (as of December 2018). While this issue is being resolved there resolved there is a workaround for deploying EAS source code.
See also EAS Issue 251: Create deployment workaround for TLS 1.2 compatibility problem
Step-by-step workaround
1. Manually download required files to a computer that has FTP access to the EAS servers.
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