We accept a range of national short-range radio certificates as long as they are valid for recreational skippers in the country you want to work and accepted by the local port authority or charter operator. Use Greece and Croatia as your reference: both expect an SRC-level (or higher) operator certificate on at least one yacht crew member.
Examples we accept (non-exhaustive):
RYA SRC (UK)
IYT VHF-SRC
FCC Restricted Radiotelephone Operator Permit (USA) plus practical VHF training from ASA/USPS or your school
SRC/Short Range Certificate issued by your national maritime authority (e.g., DK, DE, NO, SE, NL, FR, ES, IT)
LRC/GMDSS (any country): higher than SRC and fully acceptable
Croatia: "VHF" or GMDSS certificate issued by the Ministry of the Sea (often held alongside Boat Skipper B/Yachtmaster)
Greece: SRC or LRC recognised by the Hellenic authorities (any of the above typically accepted by Greek charter or port police)
What we look for:
You can perform Mayday, Pan-Pan and Sécurité correctly, manage raft and docking comms, and operate fixed and handheld sets.
Certificate should be in date (where expiry applies) and in English or with an English annotation if possible.