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From GOLD page 3-11:
3.2.1 Operational authorization to use data link
3.2.1.1 An operator intending to use CPDLC or ADS-C service should obtain an operational authorization with the State of registry or State of the operator, if required, in accordance with their rules and means of compliance. This operational authorization should address flight crew training and qualification, maintenance, MEL, user modifiable software, service agreements with the CSP, and procedures for submitting problem reports and data to the regional/State monitoring agencies. The operator should also ensure that aircraft equipment has been approved for the intended use per interoperability standards (e.g. FANS 1/A or ATN B1), described in paragraph 2.1.2, performance specifications (e.g. RCP 240 or RCP 400), described in paragraph 2.1.3, and in accordance with airworthiness requirements and related means of compliance.