Hola inner -
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FCC Radiotelephone Certificate is just a mail application. No test required.
Application paper available in schools/FAA offices.
The FCC certificate is "green" for non-US citizen and only valid 5 years.
Requires a renewal. I cannot recall the processing fee, but is not much.
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To study the written ATP material, all available on internet.
Google it for AIM "Airman Information Manual" (is in pdf) and FARs...
Regulations - study FAR 1, 25, 61, 91 and 121.
Meteorology - See difference with USA TAFs/METARs.
That is about all you need to study.
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Happy contrails