curl https://sandbox-b2b.revolut.com/api/1.0/auth/token \
  -H "Content-Type: application/x-www-form-urlencoded"\
  --data "grant_type=refresh_token"\
  --data "refresh_token=oa_sand_[...]"\
  --data "client_id=XXXX_[...]"\
  --data "client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer"\
  --data "client_assertion=long string [...]"